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Wire size for 125 Amp sub-panel used for EVSE (Electric Vehicle Service Equip.)

Wire size for 125 Amp sub-panel used for EVSE (Electric Vehicle Service Equip.)

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  #1  
Old 06-02-17, 04:58 PM
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Wire size for 125 Amp sub-panel used for EVSE (Electric Vehicle Service Equip.)

I am installing a 125 amp subpanel that will be used exclusively for charging electric vehicles at my office. It will be outside the building but in a weather-protected area. Incoming wire will be in EMT.

I have this Juicebox Pro 75 on order. I don't need anything close to that now with my Chevy Volt but I am planning to make the charger available on PlugShare.com and anyone with a Tesla will be thanking me for the faster charging speed that this unit will offer. We can expect that future electric vehicles will accept much higher charging input than the non-Teslas on the market today so I am planning ahead.

I am planning to use #2 wire of this Southwire product for the 2 hot legs.

I am unclear as to the minimum wire size for the neutral and ground conductors in this application and would very much appreciate some direction on that.

Thanks you any help that you can offer.
 
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  #2  
Old 06-02-17, 05:35 PM
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Commercial building?
Going to need a permit and a licenced electrician.
 
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Old 06-02-17, 05:53 PM
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IF the only item run from the sub-panel is the single "Juicebox" charger then you could use #4 copper conductors, depending on how far the panel is from the supplying panel. The "neutral" conductor is sized to fit the maximum unbalanced load across either of the two "hot" conductors. Assuming that the ONLY thing you will have on this panel is the charger it is probably not necessary to even have the sub-panel. In all cases, the equipment grounding conductor is sized according to the size of the circuit breaker protecting the "hot" leads. #8 copper is suitable for up to a 100 ampere circuit breaker UNLESS the "hot" leads are increased in size to allow for voltage drop. In the latter situation the equipment grounding conductor must also be increased in size proportionally.
 

Last edited by Furd; 06-02-17 at 06:11 PM. Reason: Correct misspelling.
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Old 06-02-17, 06:00 PM
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If it operates on 240 only which your link seems to indicate you don't need a neutral. Ground would be #8. You might be able to use a safety switch instead of a subpanel.
 
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Old 06-02-17, 06:14 PM
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While Ray is absolutely correct that a strictly 240 volt charger would not require a neutral, IF you install a sub-panel it is simply good practice to include the neutral. This is in case at some future date someone (maybe you) will want to add some 120 volt load.
 
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Old 06-02-17, 10:48 PM
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I would be concerned that one doesn't show any UL listing and making it publicly available.

Since they are using 6 gauge for 75 amps does that mean you need to use 90 connectors?
 
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Old 06-03-17, 05:15 AM
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75 amps is on the secondary. Current draw can be less than that if primary is wired to a higher voltage

Manufacture requires a dedicated 100 amp circuit. I doubt the charger will draw close to that at 240/208 volts, but since it is rated 100 - 250 volt, they really don't know what voltage it will be run at so they have to put that disclaimer.

I think a sub panel is a good idea. However since you really can't determine what the neutral load will be, I would recommend installing a full size neutral conductor. Ground, if used, can be #8. (If wired with EMT, the conduit is an approved grounding path.)
 
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Old 06-04-17, 08:30 AM
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Just a note of thanks to all who replied here. I hadn't checked the thread before now since I thought that I would get an email alert if anyone had posted to the thread. I was surprised to look this morning and see a half dozen responses.

Thanks specifically for the information shared and the other ways of looking at this, such as using a safety switch instead of a subpanel. The subpanel idea was intended to allow for future expansion of a 2nd EVSE down the road. Even though this EVSE could use most of the capacity of the subpanel, most vehicles on the market today would be charging at WAY below 75 amps. Juicebox has a nice current load balancing feature where two or more JuiceBox charging stations can be configured to never exceed the limit of the electrical supply circuit.

The other purpose of the subpanel was to make it easy to meter the usage with a Main Breaker Combination Service Entrance Device - since our office rent includes electricity, it is only fair to pay for the additional electricity used in vehicle charging.

I suspect that as electric vehicles become more common you will see a lot more questions here about how to incorporate these high current devices into existing electrical systems.
 
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Old 06-04-17, 09:01 AM
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This is one of the few Internet forums that require manual subscription to a thread in order to receive E-mail notification.

Note well the statement that work will require permitting and inspection and most likely will require the services of a licensed electrician. Note also that the Juice Box does not state it has UL (or other NRTL) listings or approval. This may be required by your LOCAL electrical permitting authority.
 
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Old 06-04-17, 12:09 PM
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It might be easier to install a sub meter to meter the loads rather then installing a whole new meter socket. E-mon D-mon and Leviton is one such sub meter.
 
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Old 06-04-17, 10:22 PM
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Yeah, I will probably have to call an electrician contact to at least oversee my work and pull a permit, if necessary.

I don't know what to say about the lack of UL listing on the Juicebox. These guys are one of the big players in the market and seem to be the most progressive in the industry, coming out with a 75 Amp unit (most are 30 - 40 Amps), having great cloud based PC and smart phone app control and usage logging. To the question of whether the product is UL listed, in February '17 they wrote, "The JuiceBox is not yet UL rated, but is UL compliant. It is also CE, NEMA, and SAE compliant, and EESS rated." I'm not clear on what the US requirements are on that.

I know that there are other ways to meter the consumption but this was about as cost effective as anything and it is nicely self contained in a single unit. Plus, others will tend to trust a meter that is just like the utilities use. You can buy them quite inexpensively on eBay.

So it turns out that this Main Breaker Combination Service Entrance panel does not have a non-grounded landing for the neutral. This makes sense since the neutral would normally be tied to ground as service entrance equipment. Since this is a subpanel that is not on a detached structure, the neutral should not be tied to ground, as I understand it. How would you handle that in this situation?
 
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Old 06-04-17, 10:33 PM
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On subpanels you add a ground bar and remove the bond from the neutral bar if present. All grounds go to the ground bar. There must be four wires - hot, hot, neutral, ground.
 
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Old 06-05-17, 04:20 AM
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It has been mentioned previously but IF the load is strictly 240 volts a neutral wire is not necessary.

As for "being compliant" with UL and other rating organizations the phrase is meaningless. It is ONLY after the manufacturer submits test models (often several) to the NRTL (Nationally Recognized Testing Laboratory) and the testing lab does everything in its power to cause the unit to fail in a manner that poses a hazard that a "Listing" is issued. Building to "specifications" is mostly a matter of selecting approved (by a NRTL) components and assembling in a workmanlike manner. Submitting items for testing is often not practical for the manufacturer because they only make a few of the items or they simply cannot accept the cost of the testing. In most cases a device "being compliant with the specifications IS safe but it cannot be certified as such. Some jurisdictions are very picky about only allowing "Listed" equipment being installed.

Case in point, the company I used to work for (I've been retired for 12 years now) had a cooling tower installed. The control was custom-built so it was one-of-a kind. Obviously UL listing was simply unjustifiably expensive although all the components were UL recognized for their service. The local electrical inspector, a man infamous for not deviating one period or comma from the code, refused to "sign off" the installation. My company had to bring in a NRTL field engineer who looked through the cabinet and wiring diagrams for maybe an hour. He sprinkled some holy water on it and blessed the control by affixing the official NRTL sticker on the inside door. That satisfied the local inspector who then okayed the installation. My company had to pay something like $1,000 to $1,500 for the services of the NRTL engineer.

I would hate to see you spend all the money for this charger installation and then have the local inspector refuse to okay it just because it didn't have a bona-fide UL Listing.
 
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Old 06-06-17, 11:50 AM
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I've got one other related question to the combination panel on this thread. In this case, I will be coming off of a hub on the top of this panel, going up the wall about 4' and then turning into the wall with a service entrance LB Conduit Body. Does NEC dictate any particular material for the conduit in this situation on a commercial building (Rigid, EMT or PVC), or only that it be watertight?

Thanks.
 
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Old 06-06-17, 02:39 PM
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In some places PVC is not allowed in commercial buildings, but is it not an NEC restriction so barring a local code any of those conduit types would be OK. If this is an area subject to significant damage like a truck loading dock or fork lifts operating nearby only rigid or IMC would be allowed.
 
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