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View Full Version : Sub panel generator input lines required


johnlfaz
Dec 4, 2007, 07:56 PM
Main and sub panels installed by electrician. Generator input circuit breakers installation was incomplete having no input lines to two 60 amp breakers. Connecting the generator to the sub panel via two 110v wires will power the well put but will not provide enough power to run 4 additional power requirements i.e. frig, rec room, etc. How do I run additional wires, add more breakers without shorting or compromising the sub panel.

Thanks

KISS
Dec 4, 2007, 09:18 PM
Very confused here. Can't follow. Can we assume:

The sub-panel is just for the "critical loads"?
The system uses a manual transfer switch described below.
The sub-panel has an interlocked main breaker and generator breaker so that both can't be on at the same time?
What's the generator capacity and voltage?
Is it connected all the time?
How many spaces are used/available in the sub-panel?

You realize that sum of the breaker sizes don't mean much. You can have 100 amps of labeled breakers and a 60 amp panel.

In this sort of installation, you need to be aware of the connected loads, not the breaker size. You then must ensure that the connected loads don't trip the generator breaker. So, you might have to do without well water when the fridges need to be on.

Things don't make sense because you say two 60 amp breakers. This is one 60 amp double pole 220 V breaker. It has a bar between the two breakers, so if one trips, the other one does too. This is a lot of generator capacity. It's extremely unlikely that a frig, a few lights and a well pump would exceed 120 Amps of 120V unless your counting the values on the breakers themselves.

KISS
Dec 4, 2007, 10:50 PM
Moved reply to forum:

Yes sub panel for critical loads
Understand manual transfer switch and need and no both can not be
Turned on at once
Generator capacity is 5000w voltage is one 220v, two standard 110 and
One 110 3 prong
No it is not connected all the time. Only to be used as backup power
Spaces used: two utility wires in from main breaker box each to a 60
Amp breaker
Two 60 amp breaker currently not used but meant for generator power
4 outputs wired, top two for 220 to well pump, the lower 4 for
Individual circuits.
Yes, that's what I need to know, how to wire "IN" more power than setup
Current allows with only two input locations.
As for exceeding generator output, well pump is 220 itself, furnace,
Frig and entertainment center not much alone but note that generator
Output max is 30amps. That's what I'm trying not to exceed by running only
One cord from generator to transfer box. Hope you can help. Thanks
John

KISS
Dec 4, 2007, 10:51 PM
John:
If you use "Go Advanced" you can post photo's directly to the forum.

KISS
Dec 4, 2007, 11:13 PM
5000/240 is about 20 AMPS. That should be the size of the generator transfer breaker. The utility side can be 60 amps. These two breakers must be interlocked.

Power from the generator should be wired to a generator input connector outside. You will then take the 240 outlet which should have 4 wires. One L1, L2, N and ground. L1, L2 will go to the 20 amp generator input breaker. N and ground will connect to the sub-panel. The sub panel should have an isolated neutral bar and a separate ground bar. The Neutral to Ground connection in the generator needs to be removed.

What this means is that when under utility power, 60 amps are available to the critical loads.

When power fails, you move the 60 AMP breaker to off. Turn off all the breakers in the sub-panel. The move the 20 amp transfer breaker to on.

Now, you select which circuits you want on generator power.

Does this make any sense?

KISS
Dec 4, 2007, 11:26 PM
The interlocked breakers should really be in the sub-panel. The main breaker 60 A in the sub-panel would be interlocked with a 20 amp transfer breaker. It would be fed with a 60 amp breaker in the main panel.

The other way to wire it would be to have the main breaker in the main panel interlocked to a 20 amp transfer breaker, but in this case all loads can be operated from the generator and all of the breakers but the 20 amp transfer breaker needs to be off. In this case the generator wires go to the main panel.

KISS
Dec 5, 2007, 12:51 PM
Again moved:

Simple,
I think I have enough information to run the wire I need
To the sub-panel. What I was trying to do was run multiple connections
From the generator to the sub-panel in order to power the applicance I
Consider criticle. But from what you stated, the generator is rated at
20-30 amps. That being the case, if I try and tap into multple
Outlets, I will quickly exceed the manufactures capacities. So I'll just run
One connection from the generator to the sub-panel. Just one more
Question if you please. Since I will be connecting to the 220 4 lead outlet,
Does it matter to the 220 well pump which hot wire goes to which lead?
Can I unintentionally have them backwards? Sorry for all the questions
Just trying to save a few bucks here. Besides, they didn't teach us
This in avionics school.
John

KISS
Dec 5, 2007, 01:21 PM
X and Y are interchangeable with red and black. You might try keeping them the same as the generator color codes for the coresponding terminals.

W is white and G is ground/green/bare.

The well pump doesn't matter.

The neutral conductor carries the difference of currents between L1 and L2 or X and Y.
It also makes some sense to try to distribute the 120 loads such that L1 and L2 will be symmetrically loaded with devices that you may have on together if possible.

Check your generator instructions to see if you can have all 5000 W at 120 V. Then it wouln't matter.