How many amps is my service?

Discussion in 'Electrical Engineering' started by Jones, Feb 11, 2008.

1. JonesGuest

Hello, all,

I'm getting ready to have an electrician put some 220V circuits in my
detached barn workshop. (I only have 110V right now.) I'm hoping I have
enough power running from the main panel in the house out to the
sub-panel in the barn to do what I want.

When my electrician came out to check and make sure I won't need
another/heavier wire between the house and the barn, he opened up the
sub-panel in the barn and said it looked like I have 100A service at
the subpanel in the barn.

(He said that he wanted to check at the main breaker panel in the house
to make sure 100A service was going to the barn, but he forgot to do
so.)

I just took a look in the main panel in the house, and it looks like
there is a dual pole breaker feeding the barn (I think that's the
proper term -- it's like two breakers side-by-side with the switches
connected) and each switch of this double-pole breaker is labeled 50A.

It's a Square-D panel, if that helps.

Can anyone tell me from the information I've provided what the amperage
going to the barn likely is? (Right now I have only 110V at the barn, I
believe, so please express the amperage with that in mind.) I'm hoping
I have enough capacity to have a 220V 30A circuit for a compressor and
a 220V 20A circuit for a saw (though they would never both be used
simultaneously).

Thanks for any replies.

Jones.

2. Guest

|> I just took a look in the main panel in the house, and it looks like
|> there is a dual pole breaker feeding the barn (I think that's the
|> proper term -- it's like two breakers side-by-side with the switches
|> connected) and each switch of this double-pole breaker is labeled 50A.
|
| That's only 50 amp service, not 100 amps.

However, for 120 volt loads only, it can aggregate as much as 100 amps.
Half of them would be on one pole, and half on the other. This assumes
the feed to the barn is 3-wire plus ground. It is possibly it is only
a 2-wire feed, and only providing one of the poles the breaker can do.

3. JonesGuest

OK, thanks for the replies.

I'm assuming (and hoping) that since he seemed to think I already had
100A service to the barn, that the wire from the house to the barn is
heavy enough.

Here's hoping he can just swap out the 50A dual-pole breaker for a 100A
dual pole (or whatever is needed)...

4. JonesGuest

Yeah, but at what voltage? As I said in the original post, I'm using
110V as the reference point...

5. Guest

On Mon, 11 Feb 2008 20:02:06 -0500 wrote:

| You will probably be fine with 50a at 240v unless you have several
| people working at one time. It is hard for one person to use more than
| 30 amps at a time.

Imagine running a 9600 watt heater in the barn. Now imagine running
equipment that produces that much heat just from operation.

Sometimes I wonder why we need 200 amp services to a home. Well, maybe
we need 100 amps to run air conditioners to remove the heat produced by
using 100 amps for other things.

6. Guest

| wrote:
|> On Tue, 12 Feb 2008 00:00:17 -0600, "Ben Miller" <[email protected]>
|> wrote:
|>> The protective device determines the rating. It is a 50A service,
|>> regardless of whether it is 240V 3-wire or 120V 2-wire.
|>> The difference is the maximum wattage available, not the maximum
|>> amps.
|>
|> Ben, the only reason I believe he really has 240 out there is the 2
|> pole breaker. He probably just has 120v receptacles at this point.
|
| I agree that is probably what he has. Phil seemed to be adding 50+50 to get
| to 100A, however. I was just making the point that 50A is all he has,
| assuming the conductors are properly sized of course!

Right, I was adding 50+50. If his loads are all 120 volt, and can be split
loaded well enough, then he has 100 amps worth of 120 volts, assuming he has
both poles fed in. Now that he wants 240 volt stuff, he does have to look
at it as 50 amps and needs to be sure he has both poles fed.

7. JonesGuest

Frank (any all other repliers),

Thank you very much for all of your thought, debate and replies.

I didn't mean to stir the pot, but I do appreciate all the information!

I'm hoping my electrician will come to install the circuits on
Saturday, and if he does, I will try to supply an after-action report
to fill you all in on what the final disposition was.

Again, many thanks.

Jones.