update on panel install

Well from yesterdays' thread I figured I should go look at my buddys' deal instead of guessin, so i have some questions for you guys, since I'm not real up to date on residential codes(since college in 98). I work at Hershey as an electrician mainly industrial, plc's, instrumentation that sort a thing. So here goes.

Main panel, one 2 pole 50 Amp breaker 220v. 4 wire #6 gauge fed to a JB in the basement(main is in the garage). I did a load calc based on the old Code book I have from 96. So I am puttin 3, 20 amp circuits in the 50 amp sub, total load calc 38.6 amps. Now questions.

1. Is it legal to put three 20 amp circuits in the 50 amp sub? So long as the total load doesn't exceed the 50amp?
2. I am familiar with all the grounding thats done in a factory on 480 panels, but in a house is there any additional grounding that needs to be done to the sub(ie; ground to building, pies ect?)
3. The ground on the feed is aluminum, ok?

4. Should I use no locks or another type of covering for the terminations?

Thanx guys.

-PG

The sub feed should be 4 wire with an isolated or "floating" neutral with a seperate ground bar, The box must not be bonded.

As far as I know you can place as many 20A breakers as you like in the sub as long as the total amps used does not exceed 80% of the panels rating/breaker feeding it.

If you add up the total amps of all the breakers in a main panel, most times it will exceed the main breaker/panels rating, but the actual amps used/load calc will be less.

Cass said:

The sub feed should be 4 wire with an isolated or "floating" neutral with a seperate ground bar, The box must not be bonded.

As far as I know you can place as many 20A breakers as you like in the sub as long as the total amps used does not exceed 80% of the panels rating/breaker feeding it.

If you add up the total amps of all the breakers in a main panel, most times it will exceed the main breaker/panels rating, but the actual amps used/load calc will be less.

Click to expand...

Right the load calc I got is 38.6A so 80% would be 40 on the 50 amp main, so I'm ok there.

One other question, I know you can put a bigger size breaker in the sub, but I am buyin a Square D 100 amp sub panel, and it comes with a 100 AMP main, is that ok? or should I put a 50 amp in anyway so it doesn't confuse anyone in the future

As far as I know the amperage of the breaker should correspond with the amperage rating of the wire feeding it.

Lets see what the sparkys say.

projectorguru said:

Right the load calc I got is 38.6A so 80% would be 40 on the 50 amp main, so I'm ok there.

One other question, I know you can put a bigger size breaker in the sub, but I am buyin a Square D 100 amp sub panel, and it comes with a 100 AMP main, is that ok? or should I put a 50 amp in anyway so it doesn't confuse anyone in the future

Click to expand...

You don't need ANY "main breaker" in a subpanel. It is protected by the breaker in the panel supplying the subpanel. Most people install a "main lug" panel as the subpanel. The 100 Amp breaker that you have will make a convenient switch but will not, and need not, protect anything.

I am not aware of any code requirement that limits the load to 80% of the circuit capacity. Maybe someone can find and cite the reference for me.

There is a requirement that the circuit capacity be at least equal to the sum of 100% of the noncontinuous load and 125% of the continuous load. The only continuous load that you are likely to have in a residence is an electric water heater, which is defined as a continuous load.

Bob NH said:

You don't need ANY "main breaker" in a subpanel. It is protected by the breaker in the panel supplying the subpanel. Most people install a "main lug" panel as the subpanel. The 100 Amp breaker that you have will make a convenient switch but will not, and need not, protect anything.

I am not aware of any code requirement that limits the load to 80% of the circuit capacity. Maybe someone can find and cite the reference for me.

There is a requirement that the circuit capacity be at least equal to the sum of 100% of the noncontinuous load and 125% of the continuous load. The only continuous load that you are likely to have in a residence is an electric water heater, which is defined as a continuous load.

Click to expand...

Yeah my friend wants that main sub breaker for disconnect purposes, I just didn't want to do it if its ilegal, and yes I'm installing a 100 amp main lug for this reason. Also is there a heighth requirement for the mounting?

projectorguru said:

Yeah my friend wants that main sub breaker for disconnect purposes, I just didn't want to do it if its ilegal, and yes I'm installing a 100 amp main lug for this reason. Also is there a heighth requirement for the mounting?

Click to expand...

I believe that the height requirement is that the breaker handles may be no higher than 78". That could be off by an inch or two.

There is no lower limit.