90's T&B 150A Loadcenter....Busbar Rating?

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IslanderVT

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Hi Folks,

I'm working on a job to install an EV charger in a residential garage. The loadcenter is original to the home, which was built in the mid 90's.

The service entry is buried 4/0 Al with a meter main and 200A breaker at the pole. Because of the length of the secondary's, the main panel is derated to 150A per utility requirement, and is located inside the residence. The loadcenter is in good shape and its in a clean area, so we would rather leave it as is.

The plan is to install a 48A Emporia charger to get full charging capacity of the EV. In order to achieve 48A, it needs to be hardwired, otherwise it derates to 40A if using a 14-50 socket. We plan to run 6/3 Romex through the basement, then a J-Box with polaris lugs, and a short run of exposed 6/3 MC in the garage to the charger on the wall.

The only label in the loadcenter says max capacity is 150A. No notes about busbar capacity. I would think its the same busbar as a 200A loadcenter, but it doesn't say so.

I understand EV chargers to be a continuous load. If we apply the 120% rule to the 150A loadcenter, it's only rated for adding a 30A continuous load, which is obviously a no-go for a 48A EV charging load.

My question is...does anyone know if these older T&B loadcenters use 200A (or better) busbars? If so, does anyone know of documentation on this?

We could swap the loadcenter to a new one with 225A busbars...which is probably wise...but that greatly increases the scope and cost of the job.

Thanks in advance for the insight!!
 
Since an EV charger is a continuous load, the loadcenter is limited to 120% of the total OCPD capacity of the continuous load. This means that the total current for the EV charger breaker and the main OCPD (since the same current flows through it also) is limited to 120% of the busbar rating.

If the busbar is in fact only rated for 150A, then we can only add up to 120% of that which is 180A (30A EV breaker+150A main breaker). If we follow the rule precisely, it also means that the EV charger can only run a maximum of 80% capacity of the 30A breaker, which is 24A...or 1/2 of the EV charger rating...and under 1/2 of the EV's charging rate.
 
IslanderVT said:
Since an EV charger is a continuous load, the loadcenter is limited to 120% of the total OCPD capacity of the continuous load. This means that the total current for the EV charger breaker and the main OCPD (since the same current flows through it also) is limited to 120% of the busbar rating.

If the busbar is in fact only rated for 150A, then we can only add up to 120% of that which is 180A (30A EV breaker+150A main breaker). If we follow the rule precisely, it also means that the EV charger can only run a maximum of 80% capacity of the 30A breaker, which is 24A...or 1/2 of the EV charger rating...and under 1/2 of the EV's charging rate.
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You don't derate the entire load center for a continuous load. You only derate the breaker and conductors for THAT circuit.
 
I'm thinking of this in the context of NEC 705.12(D), which is where this usually comes up. Its a common problem for PV systems backfed into a loadcenter.

We were thinking this same rule applies to all continuous loads....or at least it used to....are we wrong about this?
 
I'm just a dumb engineer, but I thought continuous loads were taken at 125%, not 120%. Also, what happened to the utility limitation of 150 A?
 
IslanderVT said:
I'm thinking of this in the context of NEC 705.12(D), which is where this usually comes up. Its a common problem for PV systems backfed into a loadcenter.

We were thinking this same rule applies to all continuous loads....or at least it used to....are we wrong about this?
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That's different. A PV system provides the panel with two power sources.

As long as adding the charger doesn't trip the main breaker, you're okay.
 
IslanderVT said:
I'm thinking of this in the context of NEC 705.12(D), which is where this usually comes up. Its a common problem for PV systems backfed into a loadcenter.

We were thinking this same rule applies to all continuous loads....or at least it used to....are we wrong about this?
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Is solar involved in this project at all?
 
Thanks everyone for the feedback...looks like we were overthinking it!

Yes, solar is included in this system, but it is line-side-tapped above the main panel, so no interaction with the loadcenter.
 
IslanderVT said:
Thanks everyone for the feedback...looks like we were overthinking it!

Yes, solar is included in this system, but it is line-side-tapped above the main panel, so no interaction with the loadcenter.
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Then 48A continuous load would be 60A breaker & conductors. As long as the entire load on the panel can take the additional load, then you're good.
 
IslanderVT said:
Thanks everyone for the feedback...looks like we were overthinking it!

Yes, solar is included in this system, but it is line-side-tapped above the main panel, so no interaction with the loadcenter.
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Yeah, I was like, why are you applying the solar 120% rule to an EV charger? Unless it's one of those inverters with an EV charger built in, they have nothing to do with each other.
 
suemarkp said:
6-3 NM cableis a problem if the load (with continuous factor applied) is 60 amps. NM is only good for 55.
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The charger is rated at 48A so 6/3 NM is OK...but right at the limit. Seems like most of them do the same.

If a NEMA 14-50 receptacle is used, it is rated for 40A because many folks see heating at the receptacle if using a standard outlet. There are better receptacles that prevent the heating, but they cost 80 bucks or more.
 
jaggedben said:
Yeah, I was like, why are you applying the solar 120% rule to an EV charger? Unless it's one of those inverters with an EV charger built in, they have nothing to do with each other.
Click to expand...

Thanks for clarifying that. For some reason I thought the same rule applied to all continuous loads. Glad it doesn't....that provides some relief.
 
There are separate 80% (125%) rules sprinkled around in the code. For example a circuit feeding a continuous load must be 125% of that load unless '100% rated' breakers are used.

Thus the reason that a 48A continuous load must be on a 60A rated circuit. See this thread:

#6 NM-B on 60 amp breaker for 48A EVSE

I have been asked to connect an EVSE to an existing piece of 6/2 NM-B (ROMEX) in a new home that was installed by the home builder. the EVSE has a draw of 48 amps, so the breaker needs to be 60 amp (48 x 1.25 = 60). My understanding is that a continues load (the charger will be drawing maximum...
forums.mikeholt.com

-Jon
 
winnie said:
There are separate 80% (125%) rules sprinkled around in the code. For example a circuit feeding a continuous load must be 125% of that load unless '100% rated' breakers are used.

Thus the reason that a 48A continuous load must be on a 60A rated circuit. See this thread:
Click to expand...

Thanks winnie...helpful information. I see now that its not allowable to size 6/3 NM up to a 60A breaker. Suemarkp was trying to say the same thing...which I now recognize.

Maybe its best to just run 6/3 MC for the whole run. It has THHN conductors rated for 90C in dry applications. Not a big adder or change to the job.

I really appreciate all the support here...you folks keep people safe...keep up the great work!
 
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