Subpanel to subpanel

[Methodical]

I have a 200 amp main electric panel box. I installed a sub panel (50 amp circuit) in my garage to feed my air compressor (30 amp). I want to install a whole house surge suppressor, but don't have any extra slots to accommodate the double breaker, nor does the box accept tandem breakers (Homeline unit), so that I could free up a couple slots. I want to install a sub panel next to the main box so that I can move a few circuits to this box to free up some slots. I also want to feed the garage sub panel from this sub panel. I've read that this can be done, but I know codes changes, so I want to be sure.

Questions.

1. Is it legal to feed a sub panel from a sub panel?

2. What amperage for the new sub panel?

3. Which surge suppressor do you recommend?

Thanks...Al

 

[Mustang51js]

Usually the bottom slots are the ones that take tandom breakers. If your putting a sub panel next to main panel I would leave garage sub in the main panel and just move a couple circuits to the sub. And last they do make surge protectors that go onto a 2 pole breaker so it doesn't take up any extra spaces in panel. Are far as sub I would just do a 60 amp if you don't plan on adding a bunch of new circuits

 

[wyliesdiesels]

1) yes needs to be 4-wire feed

2) That all depends on the calculated loads that will be connected to it

3) Eaton has a good line of surge suppressors, including electrical, telephone and CATV

 

[Methodical]

Mustang, I have an older box (at least '97). I tried the tandems on the bottom slots when I was trying to run the 40 amp circuit to the garage and no go, so I combined 2 small circuits and I had one free circuit, which allowed me to get the double pole 40 amp for the garage circuit. Your idea is a great one and I did not even think about it that way. I wish I would've seen your comment earlier, but I went out and bought the material last night for a 70-95 amp sub panel box. I already purchased the 4 gauge wire for the panel, so I am committed to doing the sub panel to sub panel now. There's not much cost difference in either approach. I will have more flexibility now.

Question can I install a surge protector on the 1st sub panel to protect the circuits on those panels including the garage panel?

Thanks for the input.

Al

 

[wyliesdiesels]

Is the #4 wire al or cu?

 

[alfredeneuman]

Question can I install a surge protector on the 1st sub panel to protect the circuits on those panels including the garage panel?

Yes you can but if you shut the subpanel off, you'll lose the surge protection to the circuits in the service panel.

 

[Methodical]

Is the #4 wire al or cu?

The wire is copper THHN rated upto 95 amp circuit.

Yes you can but if you shut the subpanel off, you'll lose the surge protection to the circuits in the service panel.

I was not clear. There will be a surge supressor on the main box. I believe the one on the main box will protect the subpanels, too, but was wandering if its a good idea or even necessary to install one on the 1st subpanel.

Thanks...Al

 

[pattenp]

4 Cu thhn is 85 amp Max.

The wire is copper THHN rated upto 95 amp circuit.

I was not clear. There will be a surge supressor on the main box. I believe the one on the main box will protect the subpanels, too, but was wandering if its a good idea or even necessary to install one on the 1st subpanel.

Thanks...Al

 

[Methodical]

4 Cu thhn is 85 amp Max.

Correction. It's the THWN-2 wire category (the category witht he 95 amp rating in the chart below)


http://www.cerrowire.com/ampacity-charts

 

[pattenp]

You aren't to use 90C for wire temp. You need to use 75C which is 85 amps for #4 Cu thhn/thwn by the NEC.

Correction. It's the THWN-2 wire category (the category witht he 95 amp rating in the chart below)


http://www.cerrowire.com/ampacity-charts

 

[Charles (in GA)]

90°C column is only for derating of wires due to temp or number of conductors in a conduit. There are no devices, switches, breakers, receptacles, etc, that are 90°C rated thus you must use the wire as if it was 75°C wire, because thats what the terminations will be.

Charles

 

[dslabuda]

So what size breaker are you going to use to feed the new subpanel?

Sent from my SAMSUNG-SM-N900A using Tapatalk 4

 

[wyliesdiesels]

You aren't to use 90C for wire temp. You need to use 75C which is 85 amps for #4 Cu thhn/thwn by the NEC.

And this is just the reason why i asked what kind of wire he is using. Most DIYers mistakenly use the 90* c column!

 

[Methodical]

So what size breaker are you going to use to feed the new subpanel?

Sent from my SAMSUNG-SM-N900A using Tapatalk 4

I want use the max that I can use. Which one do you'll suggest?

Thanks...Al

 

[pattenp]

I want use the max that I can use. Which one do you'll suggest?

Thanks...Al

If you're still talking #4 Cu THHN then the amp rating @75deg,C is 85 amps. By NEC, you can use the next standard size breaker which is a 90A.

 

[Methodical]

If you're still talking #4 Cu THHN then the amp rating @75deg,C is 85 amps. By NEC, you can use the next standard size breaker which is a 90A.

Cool.

Thanks...Al