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Bootes · May 4, 2009, 07:08 PM

A friend who is an experienced (not not licensed) electrician helped me install a sub panel last weekend and I'm a bit confused about the way he did it. He ran 2 hots 1 neutral and 1 ground between the panels (#6 conductors, #8 ground). He installed a new breaker (he called it a "dual pole") in the main panel. It's as wide as two regular breakers, and has two separate switches (forced to move in unison by a plastic bar). This is where the red and black hot wires get power.

Each one of the switches is marked "60". Dose this mean I can be drawing 55A from the red and 50A from the black and the breaker will not trip? And wouldn't that mean 105A through the white wire?(using my example).

Or dose this breaker trip when the sum of the currents (black + red) gets over 60A?

Thanks in advance!

Bootes · May 4, 2009, 07:09 PM

A friend who is an experienced (but** not licensed) electrician

Joshdta · May 4, 2009, 07:14 PM

No it means you get 60 amps,

Bootes · May 4, 2009, 07:21 PM

So this is correct for #6 feeders then?

Joshdta · May 4, 2009, 07:29 PM

Yes sounds right. Did he put it to anouther 60 amp breaker in the sub feed or to the main lugs at the top?

Bootes · May 4, 2009, 07:33 PM

They run to the 100A main breaker at the top of the sub panel.

Joshdta · May 4, 2009, 07:38 PM

Why did he put a 100 amp sub feed on a 60 amp breaker?? This will work just make sure not to exceed 60 amps in this pannel

ohb0b · May 4, 2009, 07:41 PM

A friend who is an experienced (not not licensed) electrician helped me install a sub panel last weekend

Already commented on by others

And I'm a bit confused about the way he did it. He ran 2 hots 1 neutral and 1 ground between the panels (#6 conductors, #8 ground).

At the main service panel, the neutral buss is bonded (connected to) the ground. This is the only place the Neutral and ground should be connected. When you install a sub-panel, you must run separate wires for the neutral and ground.

He installed a new breaker (he called it a "dual pole") in the main panel. It's as wide as two regular breakers, and has two separate switches (forced to move in unison by a plastic bar). This is where the red and black hot wires get power.

Each one of the switches is marked "60". Dose this mean I can be drawing 55A from the red and 50A from the black and the breaker will not trip? And wouldn't that mean 105A through the white wire?(using my example).

Or dose this breaker trip when the sum of the currents (black + red) gets over 60A?

The breaker has a common trip unit, if the current is greater than 60 amps in either the black or the red wire, the breaker opens both of them.

Thanks in advance!

Bootes · May 4, 2009, 07:42 PM

I questioned that myself, he said the 100A main breaker serves as a disconnect switch. I will never "trip" because its feed by the 60A breaker

Bootes · May 4, 2009, 07:44 PM

The breaker has a common trip unit, if the current is greater than 60 amps in either the black or the red wire, the breaker opens both of them.

That's what I was looking for! Thanks!

KISS · May 4, 2009, 08:53 PM

Let me add a few things here:

1. The feeds must be protected. So if the feed breaker is rated for 60 A, then the wires must be rated for 60 A or MORE. The disconnect or main breaker on the sub-panel can really be rated for anything. 15 A is pointless, 200 A may or may not be more expensive. Disconnects are required in detached structures. Main lug panels don't have an integral main breaker.

2. Ground rods are required in detached structures.

3. For sub panels the neutral to ground bonding screw is removed and usually a ground lug kit needs to be purchased. Ground and neutral must remain separate.

The age old question: Is two 60 amp breakers tied together equal to 120 Amps? No. The secondary of a 240/120 service is two 120 V secondaries.

This means that even though the primary is single phase, the secondary is two sinusoidal voltages 180 deg out of phase, so they add. AC voltages can add or subtract in series just like DC ones can. Phase matters in an AC circuit.

Now the other concept. Everything requires a reference and if the supply is a reference, then one current has to have an opposite sign of the other.

... 120 VAC ---- Breaker (60) -----
240 Vac total---------------------------------------LOAD
... 120 VAC ------Breaker(60)-----

You can see for the pic that one breaker sees 60 A and the other sees the same 60A

Now the trick. In a 240/120 panel, one leg of current is going toward ground and the other leg is going away from ground. Thus a 240 V load has no neutral component.

But if there was a 20 Amp load on L1 and a 15 a load on L2, then the difference flows in the neutral. You just have to keep your signs straight.

ohb0b · May 4, 2009, 09:23 PM

2. Ground rods are required in detached structures

Thanks. I forgot about that. I assumed the sub-panel was in the same building

Bootes · May 4, 2009, 09:41 PM

Its looking like we did just fine with our project! We installed grounding rods, and installed an additional equipment ground bus. To this bus we attached the ground from the main panel and the ground wire to the new grounding rods. We did not install the bonding screw.

I had not considered the phase difference. If I understand what you are saying, with my setup there will never be more than 60A in the neutral wire.