Main panel / Sub Panel (V2)

[jsieczko]

[We are going to try this again. I received my bachelors in electrical/computer engineering from Lehigh University in 1990 and am a member of Tau Beta Pi. I am not looking for "do it yourself advice" but have a question as a matter of intellectual and professional curiosity.]

I found it odd that my main panel had an 80 amp breaker feeding the sub-panel, but the sub-panel has a 70 amp breaker on the same feed. I would have thought that the breakers to be sized equivalently (80 -> 80). Is the step down a code requirement? Or did they just size the breaker for the anticipated load in the subpanel?

[The subpanel is grounded properly for a detached structure and I did a back of the envelop calculation for copper 3 THHN/THWN-2 wire with 2 current carrying conduits and got 85 amps, so 80 seems reasonable. The subpanel shows it was inspected.]

Joe

 

[Dennis Alwon]

I suspect the contractor didn't have an 80 amp breaker and the load wasn't greater than 70 so he/she used it

 

[Little Bill]

So is the 70A breaker being used as the main or disconnect at the subpanel?

 

[infinity]

Since you have an 80 amp OCPD at the origin of the feeder the one at the other end can be any size. Could be a 15 amp or a 150 amp or pick a size that you like. The NEC only cares about the feeder protection where it begins. Now if the panel at the other end is rated for less than 80 amps that's different. If it's a 70 amp panel then the 70 OCPD must stay.

 

[jap]

I suspect the contractor didn't have an 80 amp breaker and the load wasn't greater than 70 so he/she used it

I agree.

I'd also venture a guess that the 70 amp breaker in the subpanel is stabbed onto the bussbsars, backfed, and does not have the require hold down kit that's required for this type of installation.

JAP>

 

[jsieczko]

I agree.

I'd also venture a guess that the 70 amp breaker in the subpanel is stabbed onto the bussbsars, backfed, and does not have the require hold down kit that's required for this type of installation.

JAP>

You are exactly correct! They put the 70amp breaker onto the busbars. I expected to see the picture below. I showed the changes to my understanding of the reference design below.


.

 

[jap]

You are exactly correct! They put the 70amp breaker onto the busbars. I expected to see the picture below. I showed the changes to my understanding of the reference design below.


. View attachment 2553383

Did they put the hold down kit on the backfed 70 ?
or,
Have you had the cover off to see?

Just curious.

JAP>

 

[jsieczko]

Did they put the hold down kit on the backfed 70 ?
or,
Have you had the cover off to see?

Just curious.

JAP>

The 4 wire feed: white to lug on neutral bar, green to lug on ground bar, red/black directly to 70A breaker on bus bars. (Has a nice permit sticker on box too.) Is this ok?

 

[jap]

The wiring is fine.

I was just curious if they installed a breaker hold down kit on the 70 amp breaker.

It keeps the breaker locked in place which is a requirement when a breaker is back-fed but all too often overlooked and not installed.

JAP>

 

[jsieczko]

The wiring is fine.

I was just curious if they installed a breaker hold down kit on the 70 amp breaker.

It keeps the breaker locked in place which is a requirement when a breaker is back-fed but all too often overlooked and not installed.

JAP>

I'll look when I get home. I might have missed. There was a metal clip on the breaker itself but it did not appear to lock the breaker.

 

[powerpete69]

You are exactly correct! They put the 70amp breaker onto the busbars. I expected to see the picture below. I showed the changes to my understanding of the reference design below.


. View attachment 2553383

Just curios....why is the grounding electrode required in the remote building? Some inspectors want the neutral and ground separated and they call it a day. Others want the extra grounding electrode. Some garages for example have the electrode...some do not.

Feeding the side of the bus bars with a 70 A breaker seems feasible in theory. Is there something in the code that says you can't do that?

 

[jap]

The subpanel is located in a separate structure.
That's where the grounding requirements come into play.

As far as the hold down kit requirement for the backfed breaker, look at NEC 408.36d

Jap>

 

[Dennis Alwon]

I doubt there is a hold down kit installed. The ones I have seen only connect at the top 2 slots.... Perhaps other brands are capable of inserting the breaker anywhere on the buss.

 

[jsieczko]

Just curios....why is the grounding electrode required in the remote building? Some inspectors want the neutral and ground separated and they call it a day. Others want the extra grounding electrode. Some garages for example have the electrode...some do not.

Feeding the side of the bus bars with a 70 A breaker seems feasible in theory. Is there something in the code that says you can't do that?

NEC article 250.32 covers the separate ground. Has to do with the subpanel being a detached garage and other wires (like Cat 5e) cable coming over from main building. Subpanel gets grounded to both main building ground and grounding electrode in garage.

 

[jsieczko]

The subpanel is located in a separate structure.
That's where the grounding requirements come into play.

As far as the hold down kit requirement for the backfed breaker, look at NEC 408.36d

Jap>

To satisfy your curiosity, there is no BR Hold Down Bolting Screw Kit installed. This is a nice metal bracket on the breaker but near as I can tell, it performs no useful function.

 

[LarryFine]

That clip is provided to allow a padlock to be used for lock-out purposes.

 

[Dennis Alwon]

I bet the contractor thought that was a hold down mount or something. As Larry said that is to install a lock so the breaker would stay off if you were working on it.

 

[infinity]

To satisfy your curiosity, there is no BR Hold Down Bolting Screw Kit installed. This is a nice metal bracket on the breaker but near as I can tell, it performs no useful function.

View attachment 2553396 View attachment 2553397

Do you have a photo of the enitre panel without the cover?

 

[jsieczko]

Thanks everyone. Looks like I'll be buying an Eaton BR Plug-On Neutral Hold Down Kit for 2 Pole-Circuit Breaker to comply with NEC 408.36d

 

[jsieczko]

Do you have a photo of the enitre panel without the cover?

I'm going to replace the 70 amp with an 80 amp breaker to match the breaker at the main (see above), and I am going to install the hold down kit. (In case you're curious, the 60 amp breaker goes to a Tesla charger which draws at 80% or 48 amps.)

I'll probably pull a permit and have it inspected.