Trying to read voltage and amps on VA meter for Menards Power Adaptors

I'm still curious on the voltage drop of the Menards 4006 adapter as you add buildings.  Before you go cutting wires and making terminal strips or whatever, do the supplied 1-to-3 way cable separate?  If so, what kind of connectors are used?

You said you have 4 of these 3-output adapters?  If it comes apart at the arrow and has the "right" connector arrangement, I'm thinking you can take the 1-to-3 way splitter cabling from an unused adapter and attach it to one plug of the powered adapter.  You now have a 5-output adapter...2 plugs with original length, 3 plugs with essentially double-length.  Now you can measure the voltage with 1,2,3,4 buildings attached. 

There are also all kinds of splitter cables available that you could attach to one of the 4006 outputs and make it into 2,3,4,etc. outputs.  And even extension cables.

So if indeed your buildings are "low power" and you can operate more than 3 per adapter, using some combination of inexpensive splitter and extension cables is an option.  Cutting wires, splicing connections, possibly soldering, etc. can be a tedious affair.

If you are going to mess with the HO transformer, a screw-terminal adapter like this can come in handy...possibly in conjunction with a splitter-cable.

I see there are a few other threads on this issue.  Has anyone received a reply yet from Menards that clarifies the technical specs of the adapter and their buildings?  For example, the Woodland Scenics buildings I've seen state the current requirements for their buildings (50 mA, 80 mA, etc.).  Obviously this goes a long way toward choosing a suitable power source.  If you have 3 buildings each having only have a few LEDs in them, it does seem odd that Menards' suggested solution is a 3-output 2000mA adapter (unregulated).

I tried a second building on my 3-way Menards power supply.  The voltage dropped from 7.05 with one building to 5.83 with two buildings.

Bill

Hi Stan, I'll check to see if I can follow your suggestion on using the other adaptors. What web address sells all those nice extension cables? That's neat.

As far as I know Menards has not responded to the general forum inquiry, and they haven't gotten back to me on my question. Their website for each building only states that the buildings take a 4.5 volt adaptor. Unfortunately, I've thrown away all those clamshell plastic containers the buildings came in...if anyone still has them can you share what the voltage amperage ratings are for the buildings you have, assuming their even listed on the packages. Thanks.

And, thanks to everyone in their sharing of electronics information. Maybe we'll be able to help others too.

The splitter cables, extension cables, and screw-terminal adapter examples I've referred to are from eBay.  For example, just search eBay for "2.1mm splitter cable" and you'll get thousands of choices most from Asia.  You can narrow it down to "US Only" sellers which improves on the ~3 week delivery time from Asia though prices adjust upwards.  I guess the point is this style of connector is used in many electronic products so it's likely there are products that will apply to Menards buildings. 

While waiting for Menards to clarify the apparent compatibility issues between their buildings and adapters, are you "done" with the original topic of measurement technique(s)?  I think there are 2 separate albeit related issues...1) how to measure the voltage and Amps (per title of this thread) and 2) what to do about it.

I think you have the voltage measurement issue under control.  Measuring current is a different matter.  Assuming your HF meter's current measurement mode is functional are you interested in going down that path?

Stan, I think I am good on voltage measurement with the two meters I have, thanks again.

For current measurements, I am unsure what to do. I have 3 different Menards transformers: 2 are rated at 4.5 volts and 1000 mamps each (models 4002 (3 plug) and 4005 (single plug); the newer model (4006 - 3 plug) is rated at 4.5 volts and 2000 mamps. The reported problems with burned out buildings have been reported on that newer model. Previous (about a year ago) reports were that the older 4002 3-plug unit put out "unregulated" voltage. I contacted Menards last year about those reports and Ray from Menards said he hadn't heard of any problems with them, and there were thousands sold. He said the only changed suppliers and the 4006 model replaced the 4002, that's all.

Is there any need to measure current load once I get the plugs wired into each other or a terminal strip? If I understand right, the buildings will only draw enough current each needs, and that the Menards transformers won't put out excess current (but obviously will on voltage). If it is a good idea to check current then I use the meters to see what it is, once I get the wiring fiasco under control (will try to do that this weekend and I am off work tomorrow).

Paul, given my explanation above (somewhere) of how LED resistors could go poof, keeping voltage under control should be more important.  I would recommend searching flea bay for 4.5V regulated supplies with 2-3-4 amp rating. There are two styles either will work for Menards and anything else (Lemax houses and animations) requiring 4.5VDC.  One type is linear which has big transistors controlling voltages but get warm (or hot), and switchers that run cooler. Usually tell switchers because they are relatively small and compact while having a large current output at designed voltage and can usually be plugged into wall outlet (cavet, read specification or ask seller what type technology is used. If don't know then skip them and move on).  Linears are larger bulkier and generally can't be plugged directly into wall outlet like a switcher can.

My 2.5 cents.

PS I am starting another thread for the electrical gurus about USB chargers

stan2004 posted:

I'm still curious on the voltage drop of the Menards 4006 adapter as you add buildings.  Before you go cutting wires and making terminal strips or whatever, do the supplied 1-to-3 way cable separate?  If so, what kind of connectors are used?

You said you have 4 of these 3-output adapters?  If it comes apart at the arrow and has the "right" connector arrangement, I'm thinking you can take the 1-to-3 way splitter cabling from an unused adapter and attach it to one plug of the powered adapter.  You now have a 5-output adapter...2 plugs with original length, 3 plugs with essentially double-length.  Now you can measure the voltage with 1,2,3,4 buildings attached. 

There are also all kinds of splitter cables available that you could attach to one of the 4006 outputs and make it into 2,3,4,etc. outputs.  And even extension cables.

So if indeed your buildings are "low power" and you can operate more than 3 per adapter, using some combination of inexpensive splitter and extension cables is an option.  Cutting wires, splicing connections, possibly soldering, etc. can be a tedious affair.

If you are going to mess with the HO transformer, a screw-terminal adapter like this can come in handy...possibly in conjunction with a splitter-cable.

I see there are a few other threads on this issue.  Has anyone received a reply yet from Menards that clarifies the technical specs of the adapter and their buildings?  For example, the Woodland Scenics buildings I've seen state the current requirements for their buildings (50 mA, 80 mA, etc.).  Obviously this goes a long way toward choosing a suitable power source.  If you have 3 buildings each having only have a few LEDs in them, it does seem odd that Menards' suggested solution is a 3-output 2000mA adapter (unregulated).

The barrel connector size for the Menard's buildings is 5.0mm o.d x 2.5mm i.d.  I've purchased a few at Radio Shack  #274-1568.  Can't really help you with other spec's as I have a 5V DC bus (computer power supply) around the layout and hook up to it using a single dropping diode.  I do the same with all of the Miller Engineering signs.  Hope this helps a bit.

Bruce

SandJam posted:

...They may well be able to handle much higher voltages than what the adapter is labeled.  

Exactly.  This is why I'm most curious to hear what Menards has to say.  I've got to believe they have way more data points (e.g., number of returns or complaints) than the anecdotal reports here.  So if they have sold thousands of these adapters and buildings, there is probably more to the story than we are seeing. 

Earlier it was asked if the brightness of the buildings changed as the number of buildings attached changed.  Apparently the buildings had constant brightness even with changing voltage; this is an indicator that the buildings were designed to handle higher/varying voltages.

BruceT47 posted:

The barrel connector size for the Menard's buildings is 5.0mm o.d x 2.5mm i.d.  I've purchased a few at Radio Shack  #274-1568...

OK.  Then my references to 5.5mm / 2.1mm are incorrect and any connectors/cables/adapters need the dimensions Bruce says.  Size matters !

"Earlier it was asked if the brightness of the buildings changed as the number of buildings attached changed.  Apparently the buildings had constant brightness even with changing voltage; this is an indicator that the buildings were designed to handle higher/varying voltages."

I've been experimenting today and I put two buildings on the single adaptor (110 ma).  The voltage dropped to 4.5 and the lights were clearly dimer.

Bill

stan2004 posted:

BruceT47 posted:

The barrel connector size for the Menard's buildings is 5.0mm o.d x 2.5mm i.d.  I've purchased a few at Radio Shack  #274-1568...

OK.  Then my references to 5.5mm / 2.1mm are incorrect and any connectors/cables/adapters need the dimensions Bruce says.  Size matters !

I'm using 5.5/2.1 mm. They seem to work fine. And are the same ones that Miller Engineering uses.   Also 274-1568 doesn't come up on Radio Shack's site.

cjack posted:

stan2004 posted:

BruceT47 posted:

The barrel connector size for the Menard's buildings is 5.0mm o.d x 2.5mm i.d.  I've purchased a few at Radio Shack  #274-1568...

OK.  Then my references to 5.5mm / 2.1mm are incorrect and any connectors/cables/adapters need the dimensions Bruce says.  Size matters !

I'm using 5.5/2.1 mm. They seem to work fine. And are the same ones that Miller Engineering uses.   Also 274-1568 doesn't come up on Radio Shack's site.

OK.  I just checked one of the buildings and you are correct that the 5.5/2.1 MM does fit and is likely the best selection.  The 5.0/2.1 MM also seems to fit.  It looks like the heavy side spring loading on the female connector allows the 5.0 / 2.5 MM I.D to work also, but admittedly not the best fit.  I just grabbed one out of the parts bin, hooked it up and the lights came on so I stuck with it on later buildings.  

I googled the part # I posted and it came up as a valid RS part, however it is in their old red / white plastic package so the number may now be obsolete.

I'll definitely go with the smaller 2.1 MM I.D. in the future!  Don't want the lights to start flickering when it gets windy.

ogaugenut posted:

"Earlier it was asked if the brightness of the buildings changed as the number of buildings attached changed.  Apparently the buildings had constant brightness even with changing voltage; this is an indicator that the buildings were designed to handle higher/varying voltages."

I've been experimenting today and I put two buildings on the single adaptor (110 ma).  The voltage dropped to 4.5 and the lights were clearly dimer.

Bingo.  Thank you ogaugenut for the new info!

With 2000 mA 3-way adapter, 2 buildings have an output voltage of 5.83V.

With 1000 mA 1-way adapter, same 2 buildings have an output voltage of 4.5V and dimmer.

Building brightness is indeed dependent on input voltage above 4.5V.  Albeit a sample of 1, the stars are starting to align.  I don't have any Menards buildings but (in my opinion) you guys that do should be wary of using the 3-way adapter with your buildings until you hear from Menards.  Please post here what they have to say about this! 

Having taken off today I was able to get 5 buildings wired to a terminal strip powered by one Menards 4006 adaptor (2 amp) and the voltage at the strip only dropped to 6.4 volts - lights were still fairly bright! All five buildings however only have 2-3 LEDs per structure, thus its not a tremendous load. I am measuring voltage at the right spot, right? Or, should I measure at the furthest away building plug?

My next job will be with the Power station - that building alone has at least 20 LEDs ~ which is roughly equivalent to the load of 7-10 regular structures. It is on the other side of the basement, however, so it'll probably have to have its own power source. I got plenty of Menards adaptors left, running out of barrel jacks, though, but Radio Shack is not too far away.

.

As discussed earlier, for the amount of current (minimal) your 2-3 LED buildings consume, the voltage difference (drop) from the terminal strip to the building plug will be negligible for 15 ft of wiring - under 0.1 Volts.

I believe ogaugenut said he also has the Menards Power Station.  Based on his info and your latest measurements, I'd guess your 5 buildings use less than 25% of the capability of the 4006 adapter.  The voltage drops to the desired 4.5V DC when you draw about 100% of the adapter capability.   rrman did some nice calculations earlier and I'd say you're driving your LEDs twice as hard as they were designed for.  Do you happen to have any of the 1000mA adapters?  Simply using one of those for your 5 buildings will probably yield a voltage of around 5V which would drop brightness and make me more comfortable.  Otherwise, since you apparently cut the cords and are using terminal strips, can you add a few components to the strip?  Specifically you could add some 25 cent diodes to drop the DC voltage about 0.7 Volts per diode...so 3 diodes would drop about 2 Volts and you'd be near 4.5V.  Or you can add a low-voltage incandescent bulb or bulbs to the terminal strip to draw current and hence lower the voltage.

My understanding of the origins of 4.5V DC "standard" for buildings and accessories is from using 3 x 1.5V batteries.  Remember how these adapter used to be called "battery-eliminators"?   Anyway, 4.5V DC regulated adapters are hard to find...whereas 5V DC regulated adapters are everywhere and inexpensive since 5V is a standard voltage used in computer/electronic gadgets.  So if messing with diodes or other voltage reduction ploys is messy, I'd rather see you use a low-cost 5V adapter than over-driving your buildings with 6.8V.

Stan, last night I found that I have 2 additional small Menards buildings I can gang onto the existing 5 building strip - that would make 7 buildings on the strip. I also have Menards 1 amp adaptors. Am wondering if I should swap out the 2 amp adaptor first for the 1 amp or add the 2 other buildings to 2 amp supply to see what the voltage reads, if its still high then swap out for 1 amp. Actually, I am not sure about where to place the 2 other buildings, so maybe I should swap out the 2 amp...have to do some city planning.

I think both 1000mA and 2000mA adapters will still put out more than 4.5V DC even after adding 2 "small" buildings - "small" being only a few LEDs as opposed to the ~20 LED Power Station.  Here's what I think is going on:

As you've measured, the voltage drops as you add buildings which of course adds load current.  The adapters drop to the specified 4.5V when the load reaches the adapter's nameplate current.   For the same set of attached buildings, the 2000 mA will put out a bit more voltage than the 1000 mA adapter.

As shown in the crude plot, I believe you are operating well below 1000 mA.  And even adding two "small" buildings will only move you right a small amount so that your voltage will still be well above 4.5V with either adapter.

If you don't want to complicate matters with eBay regulator modules, diodes, dummy lamp loads, whatever, then I'd use the adapter that gets you closer to 4.5V when the desired set of buildings is attached.

Not to 2nd guess Menards, but after reading the other OGR threads about the building light failures, it seems they have a bit of a conundrum.  As you've already pointed out, some buildings can have 10 times the number of LEDs as another building.  And it appears they now have buildings with "neon" signs which have different electrical characteristics than LEDs.  I am now even more curious as to their response to your inquiry! 

And as far as second guessing the manufacturer goes, I think the manufacturer is smart enough to realize that this is a treasure chest of valuable research being done by competent pro bono engineer enthusiasts instead of expensive consulting engineers.

cjack posted:

And as far as second guessing the manufacturer goes, I think the manufacturer is smart enough to realize that this is a treasure chest of valuable research being done by competent pro bono engineer enthusiasts instead of expensive consulting engineers.

But Chuck, is Menards listening and using this data for planning?

Anymore, switcher technology is becoming "dirt cheap". Switcher ICs and "cookbook" schematics readily available, Just a torrid coil or transformer, capacitor, a MOSFET or two and voila, done. (OK that was simplistic but you get the idea.)  That is what I figure is inside those small cube plug in USB chargers that put out an amp or so, and I suggested (in another thread) might be a good source for powering a couple Menards LED only buildings.

 As an aside when I volunteered at a computer rebuild center, there were totes of switcher supplies from small wall warts to some big boys with serious amperages.  When that center closed I grabbed all the switcher supplies I could reasonably carry home or might ever need, including ubiquitous computer tower/desktop ones.

Paul Kallus posted:

Stan, last night I found that I have 2 additional small Menards buildings I can gang onto the existing 5 building strip - that would make 7 buildings on the strip. I also have Menards 1 amp adaptors. Am wondering if I should swap out the 2 amp adaptor first for the 1 amp or add the 2 other buildings to 2 amp supply to see what the voltage reads, if its still high then swap out for 1 amp. Actually, I am not sure about where to place the 2 other buildings, so maybe I should swap out the 2 amp...have to do some city planning.

 

 

Paul, You could probably safely use 20 mA per LED as a rule of thumb value, then add up all the LEDs of your buildings to see approximately how much current is drawn, recalling 1000 mA is = 1Amp.  So in this case ~50 LEDs would reach the adapters 1 A limit.  The "neon" sign power supplies current is much higher and seems to vary alot so don't have a rule of thumb value to factor in.

Or get fancy, measure building current draw at 4.5V and divide by number of LEDs (digital meter best bet here than analog needle). Repeat for one or two others and average the results. Probably will fall between 20-25mA range.

So curiosity led me to look at the Menards site and pasted together the "electrical" characteristics of different buildings and there's quite the range!  The Quonset Hut appears to have only 2 LEDs - perhaps like Paul's "small" buildings.  I see the Power Station which has been discussed with 20 LEDs and apparently a "neon" sign too.  And then the Train Station with 40 LEDs in the form of strip lights whatever that means.   And I saw a few buildings like the Farm Supply with an operating fan - perhaps some small motor? 

So one "building" can have 20 times the number of LEDs as another building!   And then there are the wildcards of the "neon" signs and the rotating fans. 

With this much variation, it makes me wonder if it can be as simple as saying to use the 1-plug (unregulated) adapter for 1-building and the 3-plug (unregulated) adapter for 3-buildings?!

All good points and advice.

I only have one package left (threw out all the others as they are the plastic clamshell junk) - "GrandPa's house" and it says power with 4.5 volt supply. I then checked Menards site and each building states the 4.5 volt supply as well. Simple logic dictates to supply them with as close to 4.5 volts as possible. Had I known the pitfalls of their power adaptors I would have never ordered them, and just gone with my old HO DC transformer, which I actually still may do.

Thanks again to everyone for their constructive input. I actually have two more buildings on order with Menards (had a $20 gift card that was burning a hole in my wallet). I expect them next week, and hope to have the power supply situation squared away this time next week.

Can someone who has a Menards 3-way adapter answer the questions:

 Extra credit if you post a photo!

Stan

They do come apart where you indicate, although I don't know the designation of the connector.  It is a smaller diameter than the end connectors with a yellow insulator.  Diameter appears to be about 5/32.

Bill

Stan and others, only the older 4002 3-way adaptor (1 amp) comes apart like your photo shows. The newer 4006 (2 amp) version has the 3 plugs permanently connected to the main feeder wire - and that feeder wire comes apart from the transformer.

fwiw, I swapped out the 4006 transformer for the 1-amp version and sure enough the voltage came down to around 5 volts, lights are what I call normal brightness. That's for 5 buildings.

OK guys, thanks for detailing that.  I was thinking of someone who might have an unused 4.5V or 5V regulated cell-phone charger or adapter from some gadget.  These would have just one connector output and I thought if the connectors were compatible they could at least re-use the 1-to-3 way splitter cable from the unregulated Menards adapter and be back in business with a known voltage...in my opinion of course.

I did that Stan due to the very problems cited here.  Too much voltage - almost twice as much coming from Menards with the 3 pig-tails.

Even with all the pig-tails used....still way over 4.5

I used the only one I had on hand....a Lemax 500mA.

I spliced and soldered it in (polarity matched) to the lead of the 3 pig-tails.

I'm running the burned out Engine Building (maybe 7 LEDS - no sign) and the Hermans factory (10 LEDS and the sign) with a free pig-tail.  The free pig-tail measures about 4.4 volts with the other 2 buildings fully operating.

I feel I could probably run another small building in it and still be in range but pretty close to max on this adaptor.

The building I have coming is the Chippawa with the turning fan (small motor) and a few LEDS.

What do you think that little motor might draw?

My set up with the Lemax has been running off and on now for over a week with no issues.

Dave

A small DC gearmotor assembly slowly driving a light-weight fan blade should draw no more than 50 mA...or the equivalent of about 2-3 LEDs.  If your 500 mA Lemax adapter (presumably unregulated) has already dropped to 4.4V with your existing loads I think you are indeed max'd out.

If Lemax products are readily available to you I see they have what appear to be regulated 3-output 4.5V adapters.  It's fascinating they describe it as a "switching mode" power adapter which tells a techno-type that it's regulated but I wonder what it means to a typical customer at Michael's Craft Store where I find Lemax stuff!  Yet, on their website I couldn't find the mA rating of this though on Amazon I found what appears to be the same product and it says 1000 mA.

But if you already have the splitting cabling in place and just need a more than 500 mA eBay has many 4.5V 1000mA regulated adapters for $2-3 free shipping from Asia...or $5-6 for a US-based seller.

Thanks Stan

I had checked out the 3 way ones on Michael's site and think they would work fine.

The only Menards adaptor I have/had is the 3 way one which put out twice the stated value.

I'm taking delivery this week of 2 more Menards buildings and 2 Menards individual adaptors.  (each for use on one building only).  I will measure the output of both these singles and report back.

After reading multiple posts about the power switch adapters I'm totally confused.  It seems lots of people have different ideas on what is causing this problem of not lighting, dimming etc.  We really do need to hear from Mark at Menards as to what's causing this problem.  Lighting a building without the fear of frying something or no lights at all shouldn't take up this much time on the forum.  

Paul

Harleylito posted:

After reading multiple posts about the power switch adapters I'm totally confused.  It seems lots of people have different ideas on what is causing this problem of not lighting, dimming etc.  We really do need to hear from Mark at Menards as to what's causing this problem.  Lighting a building without the fear of frying something or no lights at all shouldn't take up this much time on the forum.  

Paul

Well I pointed out in earlier entry with formulas, how higher adapter voltage could fry the small resistors that current limit the LEDs.  I and others then said the best choice is a constant voltage adapter that puts out steady regulated 4.5VDC.  The best are the switcher or switch mode adapters or a linear supply outputting that voltage. 

I don't believe that Mark or Menards has a electrical engineer on staff to answer this adapter question.  They can only go on what their Chinese supplier tells them.  Sort of like taking the diagnosis of doctor in a specialty area you are unfamiliar with.

Really, Menards is getting great pro-bono help/advice from electronic engineers and technicians on this thread and elsewhere who "have been there, done that", fried and smoked parts and designs.

Harleylito posted:

...We really do need to hear from Mark at Menards as to what's causing this problem.  Lighting a building without the fear of frying something or no lights at all shouldn't take up this much time on the forum. 

Have you sent an inquiry to Mark at Menards?  From various comments on different threads it's not clear to me if Menards sees this as just a normal return rate or warranty repair...or whether they indeed see it as a product defect or something systemic.   If most of the returns/problems are going on at the bricks-and-mortar stores I would think it could take some time for field data to make it back to headquarters.

I've already put the cart-before-the-horse and jumped to a conclusion!  They need to replace their existing adapters with regulated versions just like Lemax did for their 4.5V lighted products.  It looks like Menards uses the Masterforce private label for their electronic products.  I figure it would take months to put the pieces in place, ramp up production in Asia, get product to US shelves, etc.

I received a reply email from Ray at Menards Guest services. They will be discussing this situation with their Factory Engineers.

One thing I have learned here is that regulated power supplies are good, un-regulated not so good. 

This is for Stan, I'm jumping right behind you 

I have a building on the way. I was planning on using a PC power supply's 5VDC with a series diode. I think I''ll stick with that plan.

John H posted:

I have a building on the way. I was planning on using a PC power supply's 5VDC with a series diode. I think I''ll stick with that plan.

I assume by this statement, you mean you WILL use a PC supply.  If so, I would add a 1 or two amp fuse in series with hot wire.  Those PC supply +5VDC can really source the current!

Thanks, RRMAN. I have all my LED lit buildings on a 3A resettable breaker. I use a digital DC volt/amp meter on each circuit, so when I get up to 2500ma or so I start another circuit. I'm using the 12VDC tap of the power supply for them, with mostly LED strip lighting conversions. 5 meters of them only draw 2 amps, and I have almost used one up, so I have more on the way. I'm using 22awg wire so I limit the circuit to that. It doesn't protect each individual building, but should cover a short.

rrman posted:

John H posted:

I have a building on the way. I was planning on using a PC power supply's 5VDC with a series diode. I think I''ll stick with that plan.

I assume by this statement, you mean you WILL use a PC supply.  If so, I would add a 1 or two amp fuse in series with hot wire.  Those PC supply +5VDC can really source the current!

Not sure I understand this?  Is the fuse a backup in the event the internal protection fails?  I can ground a couple of pieces of magnet wire together on any of the outputs and my unit shuts down instantly for 3-5 minutes. Thanks for any additional input!

Bruce

BruceT47 posted:

rrman posted:

John H posted:

I have a building on the way. I was planning on using a PC power supply's 5VDC with a series diode. I think I''ll stick with that plan.

I assume by this statement, you mean you WILL use a PC supply.  If so, I would add a 1 or two amp fuse in series with hot wire.  Those PC supply +5VDC can really source the current!

Not sure I understand this?  Is the fuse a backup in the event the internal protection fails?  I can ground a couple of pieces of magnet wire together on any of the outputs and my unit shuts down instantly for 3-5 minutes. Thanks for any additional input!

Bruce

 

Hi Bruce,

Suggesting using an external fuse on each of John's 5V lines.  If your PC supply shuts down with a short on any output then you have a better designed supply than I have seen.  AFAIK, the PC supplies are made cheap as possible with just enough protection to keep UL happy.

The fuse should be sized to protect the downstream wiring, which may be fairly small gauge inside the building.  You don't want to have 10 or 20 amps available from the supply if the wire can't handle it.