Subpanel amps far exceeded by circuit amps

[Highbeam]

This must a common question....

I am wiring up my shop subpanel and have plans for lots of circuits. The total amperage of all the circuits will far exceed the 60 amp feed from the main panel. What is the code on this? Is there a percentage I can't exceed?

By the time I add up a 30 amp comressor, 5-20 amp outlet circuits, 2-20 amp lighting cicuits, a water heater, a 30 amp RV plug circuit, and a 50 amp welder circuit it seems silly to feed it with a 60. The main breaker in the subpanel acts as a disconnect since it is a 100 amp breaker but the subpanel feed from the house is 60 amp.

I'm not worried about the voltage drop or actual likelihood of popping the 60 amp feed breaker but the code about using all of these circuits. I will be getting an inspection.

Thanks folks

 

[hh76]

You are fine. The panel will have a maximum number of circuits permitted, which is probably 20 for the 100a panel. You will be under that.

 

[Steevo]

The 100A subpanel in my shop has a total of 440 amps in breakers.
No problem, because many are for receptacle circuits, welders, lathe, mill, etc. that would never all get loaded concurrently.

 

[91bronc300]

I am not an electrician (at all), but what is the point of having a 100 amp disconnect in the subpanel if the subpanel feed from the house is 60 amp?

 

[Steevo]

I am not an electrician (at all), but what is the point of having a 100 amp disconnect in the subpanel if the subpanel feed from the house is 60 amp?

The breaker at the main panel has to be matched to the wire/load and the main breaker at the sub panel only serves as a disconnect.

 

[Highbeam]

Thanks folks, I will go ahead and load up the panel with lots of circuits to make sure the loads are balanced.

It's a big panel with lots of slots. These are sold as 100 amp panels and come with the 100 amp inlet breaker included. The 100 amp breaker only serves as an on/off switch.

There are lots of very good reasons to buy a big panel. Bigger than you'll ever need. They certainly don't cost much more. In fact, I picked the biggest one on the shelf.

 

[theoldwizard1]

By the time I add up a 30 amp comressor, 5-20 amp outlet circuits, 2-20 amp lighting cicuits, a water heater, a 30 amp RV plug circuit, and a 50 amp welder circuit it seems silly to feed it with a 60. The main breaker in the subpanel acts as a disconnect since it is a 100 amp breaker but the subpanel feed from the house is 60 amp.

You do know it will be a long walk to the house if the water heater is running while you are welding and the air compressor kicks on !

Of course, you are probably smart enough to turn off the breakers for the compressor and water heater when you ARE welding !

 

[CNGsaves]

With all the items you might potentially use in garage, it makes good sense to have 100 amp subpanel . . . AND . . have the wiring from main panel capable of supporting 100 amp. Even though you currently only have 60 amp breaker at main panel feeding the subpanel, that is not problem as you can upgrade main panel later and put 100 amp breaker in to feed the garage.

Post up some pics of your garage toys . . . we like pics on GJ !!

 

[Highbeam]

You do know it will be a long walk to the house if the water heater is running while you are welding and the air compressor kicks on !

Of course, you are probably smart enough to turn off the breakers for the compressor and water heater when you ARE welding !

Yes, a long walk. Hasn't happened yet but I am aware that it could. I did use 2" conduit for the feed from the house to the shop so that I could pull bigger wire someday. And yes, the subpanel with the 100 amp inlet breaker makes the feed upgrade much easier.

Water heater is 4500 watts with no surge, welders actually use a pretty small amount of current since they weld at about 25 volts and on normal amperage settings of say 130 amps we're only talking 3250 watts. The air compressor, now that puppy has a surge. Let's just say it uses a full 7200 watts. That's 62.3 amps without even considering lights at 1 amp per fixture x 8 fixtures. Oh, and gonna need a fridge out there.

In a perfect storm, 60 amps is not enough. I will find out.

Water heaters can be put on timers and I'll have a way to turn the air compressor on/off.

The main reason for this thread though was to be sure that I could set up the subpanel properly and safely for the possible loads regardless of the feeder amperage.

 

[Charles (in GA)]

This must a common question....

I am wiring up my shop subpanel and have plans for lots of circuits. The total amperage of all the circuits will far exceed the 60 amp feed from the main panel. What is the code on this? Is there a percentage I can't exceed?

To directly answer your question, no, the NEC does not address this. With proper circuit protection, proper wire sizes, etc, there is no problem with having lots and lots of breakers and amperage ratings way beyond the main or subfeed breaker capacity

 

[Zeke]

With all the items you might potentially use in garage, it makes good sense to have 100 amp subpanel . . . AND . . have the wiring from main panel capable of supporting 100 amp. Even though you currently only have 60 amp breaker at main panel feeding the subpanel, that is not problem as you can upgrade main panel later and put 100 amp breaker in to feed the garage.

Post up some pics of your garage toys . . . we like pics on GJ !!

That's just transferring the calculation problem to the main panel. He probably has a 200A main, and a lot of house circuits including a few 240v. If he increases the garage by that much and USES it, he may shut the house down. Better to trip the 60A, IMHO.

 

[wyliesdiesels]

That's just transferring the calculation problem to the main panel. He probably has a 200A main, and a lot of house circuits including a few 240v. If he increases the garage by that much and USES it, he may shut the house down. Better to trip the 60A, IMHO.

Ive never heard of nor seen someone trip a 200a house main that matched to the correct size house. Keep in mind that things like an electric range hardly ever pull their max circuit capacity! My electric range, when baking, uses 10.5a(fed by a 50a breaker). If i turned on a few burners, the load would be closer to 20a(ive tested it with my clamp meter), but the range still wouldnt be pulling its max. Another example is my A/C compressor/condensor which is fed by a 30a circuit but barely even pulls 20a while running!

Again, it would be very hard for someone to trip a 200a main. They would have to have everthing on at the same time, which is very unlikely!

 

[ddawg16]

The proper way to do a load calc is to add up the loads that will be running at the same time. What you do for your house is different than you might do for a business....

In your garage...worse case...your running a compressor, table saw (or drill) and maybe a dust collector. And maybe a heater or AC unit. Add up those loads and you will know what your potential full load is.

Is that Sub panel set up fo 240Vac? If so....if your feeding it 240 60a from the house, then you potentially have 120A at 120 Vac....in other words, you can have up to 60A on each leg....

Say you have a 240Vac compressor that pulls 10a....that now leaves you 50A on each leg...

A good electrical layout is to try to balance all of your 120Vac loads....put half your lights on one side...half on the other leg....etc.

It's not hard to figure out.

 

[ForceFed70]

60A subpanel is plenty big for the average home garage/shop. 1 person can only use so much electricity at once. Yes, it may trip under a "perfect storm" circumstance, but in reality that almost never happens.

 

[Highbeam]

Is that Sub panel set up fo 240Vac? If so....if your feeding it 240 60a from the house, then you potentially have 120A at 120 Vac....in other words, you can have up to 60A on each leg....

A good electrical layout is to try to balance all of your 120Vac loads....put half your lights on one side...half on the other leg....etc.

Oh yes. It is a Siemens load center panel, I think 40 circuit, that is fed with 60 amps of 240. I installed it and it was permitted. I am an engineer and overanalyze these things so items like my overhead lighting are on two circuits to be sure that I evenly load both "phases" of the 240 feed.

 

[Highbeam]

60A subpanel is plenty big for the average home garage/shop. 1 person can only use so much electricity at once. Yes, it may trip under a "perfect storm" circumstance, but in reality that almost never happens.

The only abnormal thing I will have in there is a water heater which will **** up a pretty good portion of the capacity whenever it cycles. Since it cycles automtically I might have an issue.

This is not a commercial shop, just me.

Thanks for all the help folks. I will move forward with excessive wiring and circuitry.

 

[larry_g]

I am not an electrician (at all), but what is the point of having a 100 amp disconnect in the subpanel if the subpanel feed from the house is 60 amp?

One thing that is worth remembering, a breaker is in place to protect the downstream wire. So the 60a breaker in the main panel is to protect the wire that runs from the main panel to the subpanel, nothing else.

lg
no neat sig line