Main panel / Sub Panel (V2)

[powerpete69]

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

I see it in black and white.
The city inspector passed my garage panel without a grounding electrode as long as the neutral and ground are separated. Perhaps its because its a 120V, 20 amp single pole breaker feeding it. Perhaps the small single feed breaker box is just a fancy "outlet" with some 15 amp breakers to allow for existing 14 gauge wire. Which it is.

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

What is the purpose of this lock down kit? To keep the breaker from flying off in a short circuit situation due to massive magnetic force?
If that is the case, wouldn't all breakers need to be locked down?

 

[wwhitney]

The point of the hold down for a backfed breaker is that if the breaker is on and supplied with power, and it comes off the bus, then it has live exposed bus clips that can contact all sorts of things that should not be energized.

Cheers, Wayne

 

[powerpete69]

The point of the hold down for a backfed breaker is that if the breaker is on and supplied with power, and it comes off the bus, then it has live exposed bus clips that can contact all sorts of things that should not be energized.

Cheers, Wayne

Ahhhhhh.....most excellent explanation!!

 

[suemarkp]

Before you change that 70A to an 80A, are you sure there is really #3 wire feeding that panel? The diameter looks the same as that 60A circuit to the Tesla charger. A worn 6 digit can look like a 3... It appears the wire is copper. #6 copper can do 65 amps using the higher 75C temp ratings. With NM cable, it would be limited to 55A. You can round up a 65A feeder to 70A if the calculated load is 65A on #6 wire. Also, #6 (and smaller) wires can't be recolored white -- has to be native white insulation like the Tesla circuit.

If you have #4 copper feeding the panel, it is good for 85A and changing the breaker to 80 is fine, and taping wires white is fine.

 

[Dennis Alwon]

If the load is 85 or less you can install a 90 amp breaker on it. 240.4(B)

 

[Eddie702]

I ran into this with a BR main breaker panel I used for a sub panel with a generator interlock installed on the cover. The Main was 125 amp and had a hole drilled in it to secure the main breaker w.ith a factory provided screw going through the hole into a plastic clip.

The interlock kit came with a clip and screw to secure the generator back feed breaker and that's fine but The 30 amp BR I put in for the generator feed had no ho;e in it for the screw. I think the BRs only have holes in them on the larger breakers

 

[jsieczko]

Before you change that 70A to an 80A, are you sure there is really #3 wire feeding that panel? The diameter looks the same as that 60A circuit to the Tesla charger. A worn 6 digit can look like a 3... It appears the wire is copper. #6 copper can do 65 amps using the higher 75C temp ratings. With NM cable, it would be limited to 55A. You can round up a 65A feeder to 70A if the calculated load is 65A on #6 wire. Also, #6 (and smaller) wires can't be recolored white -- has to be native white insulation like the Tesla circuit.

If you have #4 copper feeding the panel, it is good for 85A and changing the breaker to 80 is fine, and taping wires white is fine.

The 60amp circuit is definitely #3

 

[jsieczko]

If the load is 85 or less you can install a 90 amp breaker on it. 240.4(B)

That would be great. I was planning on putting an 80amp on the feed to match the breaker in main panel, a hold down to make it conforming to code, and a 70 amp on the tesla charger (which will draw 20% less or 56amp). If I could put a 90 amp on the 3 gauge, I could put an 80 amp on the tesla charger which will draw 64 amps.

Its a 150' run at 3 gauge. I was planning to be a little more conservative, leave the backfeed at 80a and tesla charger at 70a which will draw 56a.

Can I really push the 3 gauge that much? Sustained 64 amps for a couple hours. If it was me, I would have run #2 or better in the conduit, but #3 is what is there.

 

[jsieczko]

If the load is 85 or less you can install a 90 amp breaker on it. 240.4(B)

Dennis,

I looked at 240.4(B). 240(b)(1) says the conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug connected portable loads. Since the 80amp breaker in the main panel supports a sub-panel in a garage with lights, multiple receptacles, in addition to the tesla charger, I think I don't meet the requirement to put a 90amp breaker on it.

Am I reading this wrong?

 

[Dennis Alwon]

Yeah, you are wrong LOL... The feeder is not part of a branch circuit it is a feeder. The fact that there are branch circuits in the panel is not an issue

(B) Overcurrent Devices Rated 800 Amperes or Less. The
next higher standard overcurrent device rating (above the
ampacity of the conductors being protected) shall be permitted
to be used, provided all of the following conditions are met:
(1) The conductors being protected are not part of a branch
circuit supplying more than one receptacle for cord-andplug-
connected portable loads.
(2) The ampacity of the conductors does not correspond with
the standard ampere rating of a fuse or a circuit breaker
without overload trip adjustments above its rating (but
that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed
800 amperes.

 

[Dennis Alwon]

Just remember if the calculated load is greater than 85 then you cannot put it on a 90 amp overcurrent protective device.

 

[robertd]

Why is there a 1/2 EMT clamp holding down wires in the top of the panel?

 

[LarryFine]

Why is there a 1/2 EMT clamp holding down wires in the top of the panel?

Someone didn't use the natural curl of the stranded conductors to keep them dressed correctly.

 

[Fred B]

Why is there a 1/2 EMT clamp holding down wires in the top of the panel?

Someone didn't use the natural curl of the stranded conductors to keep them dressed correctly.

Is there anything in the code that would either restrict or permit this? Code reference please. I've seen this before but not sure. I've had times I would have loved to do this like on unruly feeders.

 

[retirede]

Is there anything in the code that would either restrict or permit this? Code reference please. I've seen this before but not sure. I've had times I would have loved to do this like on unruly feeders.

I’ve seen zip ties with integral screw holes used this way also. It would seem that’s exactly what they’re made for.

 

[robertd]

I’ve seen zip ties with integral screw holes used this way also. It would seem that’s exactly what they’re made for.

They are designed to secure wires, an EMT clamp is not. What worries me is the clamp could have a sharp edge to cuts into the insulation.
The only "code" problem would be it's not being used per the manufacturers instructions, and / or it's not listed to clamp wires, only EMT.

 

[PatrickGoodyear]

I have a question/situation related to this: The utility has installed a meter main and disconnect next to their pad mounted transformer. However, the actual service is needed 500 feet away. So we up size the conductors for voltage drip, and run 500 feet. Is it better to install a neutral ground bond in the subpanel 500 feet away from the service equipment, run an appropriately sized equipment grounding conductor 500 feet, or both? It seems like the multiple path issue wouldn't apply here as there is no other metallic connection between the two sites. I'm thinking no equipment grounding conductor, and re-ground the neutral at the sub-panel. The use case is a remote cellular site. so there will be a complete ground ring system 500 feet away from the meter main. Thanks in advance for your help.

 

[LarryFine]

I would opt for running it as a service as opposed to a feeder, and not running a separate EGC.

Which means bonding at the load end. There should be no issue bonding at the source end, too.

 

[mikeames]

a 70 amp on the tesla charger (which will draw 20% less or 56amp). If I could put a 90 amp on the 3 gauge, I could put an 80 amp on the tesla charger which will draw 64 amps.

Where are you getting this 20% less idea? Generally the charger will draw what it wants. It does not know what size breaker its on. If you put it on a 1000A amp breaker it would draw the same as if it were on a 40 amp breaker. Unless Tesla chargers are programmable( ie: you tell it the breaker size and they auto adjust draw) I mention this because you used the numbers 70 and 56 which is 20% less and you used 80A and 64, also 20%. Generally circuits are sized where the breaker is 125% greater than the calculated load or the load is calculated to be 20% less than the breaker size. That does not mean the load will actually draw that. I know nothing about Tesla chargers, but based on their largest charger it only draws 48 amps. Increasing that breaker size is fine but it wont change the performance of the charger.

I did note that there is commission programming for circuit size, but he max is still 60/48 amps

page 7 manual for circuit sizing https://www.tesla.com/sites/default...ng/Gen3_WallConnector_Installation_Manual.pdf

 

[Dennis Alwon]

Where are you getting this 20% less idea?

I think he is talking about 80% of the overcurrent protective device which is 56 amps