When is 100 amps to small

[Mark P]

I am surprised to find a 2440 SqFt house built in 1995 w/ only 100 amp service.

It has the following electrical appliances:

- dryer

- a/c

- range/oven

- microwave

- garbage disposal

- dishwasher

Using one of the free online load calculators it came up with a minimum service of 181 amps.

I verbally explained that it is very unusual for a house of this size and age to only have 100 amps service, but I could not necessarily say it would be inadequate. That would depend on what all was to be installed when they moved in.

So my question is how do I write this up? Do I just explain that it is unusually small and maybe inadequate or do I call for a sparky to perform a load test?

I’m not quite awake yet, but this is what I have now

“FYI: The house’s electrical service is 100 amps. This is unusually small for a house of this size and age. A typical house of this size and age has 200 amps to adequately provide for all the electronics of a modern house.â€

[kurt]

It's not electronics that are the problem; electronics (computers, stereos, etc.) use teeny tiny amounts of power.

Electrical components are a problem. I usually phrase it somewhere along the lines of "100 amps is too small for modern use needs", or something like that.

And, it's not a load "test". It's a load calculation.

After that, I just tell them it's probably too small, and they will likely want/need a larger service to accommodate lots of appliances, if lots of appliances and devices is what they're into.

[Tom Raymond]

Looking at SquareD QO load centers, the 100 amp panels are available with 12, 16, and 20 circuits, with one odd panel at 32 but the cover is sold separately. They do not allow tandems. My smallish kitchen has eight circuits (with a gas range) and I skimped at least one circuit. With your list of 6 appliances at least 5 should have dedicated circuits and 2 of those are doubles, that's 7 spaces in the panel already. It's definately small for the size of the house, but I think it's more of a convenience issue than a safety concern.

Tom

[Jim Katen]

I am surprised to find a 2440 SqFt house built in 1995 w/ only 100 amp service.

It has the following electrical appliances:

- dryer

- a/c

- range/oven

- microwave

- garbage disposal

- dishwasher

Using one of the free online load calculators it came up with a minimum service of 181 amps.

I think you erred. I just ran two different calcs and came up with 92 amps for the first & 115 for the second. I think that a 100-amp service is probably a close thing on that house.

I verbally explained that it is very unusual for a house of this size and age to only have 100 amps service, but I could not necessarily say it would be inadequate. That would depend on what all was to be installed when they moved in.

So my question is how do I write this up? Do I just explain that it is unusually small and maybe inadequate or do I call for a sparky to perform a load test?

I’m not quite awake yet, but this is what I have now

“FYI: The house’s electrical service is 100 amps. This is unusually small for a house of this size and age. A typical house of this size and age has 200 amps to adequately provide for all the electronics of a modern house.â€

[Billy_Bob]

100 amps is too small if you keep tripping the main breaker because you are using more amperage than that at the same time!

But if you never trip the main breaker, it is fine.

And one family living there may never trip the main breaker, yet another family might trip it everyday.

Basically it is what all you have tuned on "at the same time".

My favorite for designing these things and thinking about how much total amperage will ever be needed is the "thanksgiving test"...

You have all the kids in their rooms with everything on playing with their gizmos.

Adults in the living room with everything on.

The "in-laws" have their RV pulled up to the garage and plugged in.

Grandpa is out in the shop with someone seeing how that new table saw cuts wood and trying out other power tools.

Then there are 3 people in the kitchen cooking up a feast with every gadget known to man going full blast. Range, dishwasher, refrigerator because door is constantly open, garbage disposal, water heater, blender, bread maker, microwave, etc.

Then pop goes the main breaker!

[Mark P]

Thanks everyone, another day in TIJ school.