Wiring gauge for 30A L2 EVSE? Electrician used #10?

[billg]

Bill, I searched and couldn't find the install instructions for that unit on their webpage. Does that unit have any pilot level settings (I.e. Can it be set to advertise different charging levels? I looked at that unit at Home Depot years ago and I can't remember if it did.

Thanks
Alan

On the Product Overview page, look for the "Info and Guides" box. It has 4 pdf files including installation instructions. I knew where to look because I helped a friend install one of these for his Leaf. Maybe you'll find what you're looking for in one of those files.

 

[CharlesinGA]

Article 625 of the National Electric Code clearly defines EVSE's as a continuous load, NO EXCEPTIONS. Thus a 30/32 amp output EVSE needs a 40 amp circuit which is #8 wire and 40 amp double pole breaker. DO NOT use a GFCI breaker, very expensive and defeats the purpose of the EVSE which has GFCI capability with 4X auto reset in one hour before complete shutdown. Use copper wire.

In the NEC certain other things, mostly heating devices (air and water) are classified as continuous ALWAYS, and then anything that is expected to be on for more than THREE hours, ie office lighting on all day.

Charles

 

[tkdbrusco]

Went through this myself trying to use an available dryer outlet. A 30AMP L2 will pull a continuous load and therefore even though 10AWG is stated to be enough for 30AMP circuits, it is only suited for up to 24AMPs of continuous draw. You need to have 8AWG to be up to code. Our run was so short that our electrician said we'd likely be fine with 10AWG, but I would rather be safe and not have my house burn down.

 

[AlanSqB]

Agree in full. Pull the right gague, get a permit, get an inspection if you are getting an install.

However, if you already have a 30a circuit to work with, like a dryer outlet, you will be fine with an EVSE that can be set down to 24a or less. You won't miss those extra 3.5a in an overnight charging situation. Don't feel like you have to run all new copper and conduit if you already have an unused dryer outlet in your garage. Just make sure you use an EVSE that can work safely on it.

For example, clipper creek makes a unit that has a NEMA 14-30 plug that is set down to 20a by default. The EVSE upgrade by Ingineer is another great option. Most wall mounted EVSE have the ability to have their pilot signal adjusted to limit their output.

In this case I think the OP did exactly the right thing by getting the electrician out for a repull. It was paid for and should have been done right in the first place.

 

[iluvmacs]

Bill, I searched and couldn't find the install instructions for that unit on their webpage. Does that unit have any pilot level settings (I.e. Can it be set to advertise different charging levels? I looked at that unit at Home Depot years ago and I can't remember if it did.

No, the EVlink cannot be dialed back.

 

[GlennD]

Worst case you could drop in a OpenEVSE ver 4 board. With the LED board it would be under $100 assuming that the GFCI coil and contactor are reusable. It could be set for any default current up to 80A. For sure it supports 24A. In fact with a display and button you can set the current in 2A steps. Much easier to mount the LED board in an existing housing.

I repaired an out of warranty Aeroenvirment one this way. It was a drop in replacement. I had to add a relay with my DIY ver 2 board but the ver 4 board would have fired the contactor directly through its built in AC driver.

 

[Valdemar]

While it is reasonably safe I wonder if placing a device capable of continuous draw of more than 24A, even if it is dialed back to 24A, on a #10AWG circuit is code-compliant. Also would be interesting to know what would your home insurance say in an event of a fire if they can link it to using non-UL approved or modified equipment. Just saying...

 

[wwhitney]

While it is reasonably safe I wonder if placing a device capable of continuous draw of more than 24A, even if it is dialed back to 24A, on a #10AWG circuit is code-compliant.

Sure it is. Any device is capable of drawing more current that it is designed for, it could have an internal short. If the device is configured for 24A continuous, and it is properly supplied with #10 copper on a 30A breaker, it is code compliant. We don't have to worry about the "what if" someone else reconfigured it to more than 24A, that person would be responsible for rewiring the branch circuit appropriately.

Cheers, Wayne

 

[Valdemar]

While it is reasonably safe I wonder if placing a device capable of continuous draw of more than 24A, even if it is dialed back to 24A, on a #10AWG circuit is code-compliant.

Sure it is. Any device is capable of drawing more current that it is designed for, it could have an internal short. If the device is configured for 24A continuous, and it is properly supplied with #10 copper on a 30A breaker, it is code compliant. We don't have to worry about the "what if" someone else reconfigured it to more than 24A, that person would be responsible for rewiring the branch circuit appropriately.

Cheers, Wayne

I don't think an internal short is a good analogy as this would be mitigated by the OCPD. The code is full of requirements that are based on "what ifs". For example, when installing solar you need to size your solar feed breaker and wiring based on the inverter AC power rating and not the max DC power that your solar can technically create which can be much lower when you undersize the array relative to the inverter. And it does take lot more effort to increase the size of the solar array than to misplace a jumper inside the EVSE.

 

[wwhitney]

I don't think an internal short is a good analogy as this would be mitigated by the OCPD.

So would a 30A continuous load on a 30A breaker on #10 copper. The weak link in that chain is the breaker--it is only supposed to hold indefinitely at 40C ambient temperature with 24A continuous load, and is allowed to trip with a higher continuous load. So the reason to upsize circuits for continuous loads by 125% is to avoid tripping the breaker--the wiring is rated to handle its full ampacity all day long. If you got a special 100% rated 30A breaker (which would be in its own enclosure and might cost more than the EVSE, if it exists), you could run 30A continuous on #10 copper code compliantly.

The code is full of requirements that are based on "what ifs".

That may be, but we can stick to the code required "what if" considerations. For an EVSE jumpered to 24A, it is compliant to install on a #10 copper with a 30A breaker. Unless you have a citation for some requirement I'm not familiar with?

Cheers, Wayne

 

[Valdemar]

I don't think an internal short is a good analogy as this would be mitigated by the OCPD.

So would a 30A continuous load on a 30A breaker on #10 copper. The weak link in that chain is the breaker--it is only supposed to hold indefinitely at 40C ambient temperature with 24A continuous load, and is allowed to trip with a higher continuous load. So the reason to upsize circuits for continuous loads by 125% is to avoid tripping the breaker--the wiring is rated to handle its full ampacity all day long. If you got a special 100% rated 30A breaker (which would be in its own enclosure and might cost more than the EVSE, if it exists), you could run 30A continuous on #10 copper code compliantly.

I'm not necessarily disagreeing on the 30A+ EVSE set to 24A being compliant on a #10/30A breaker circuit, but as for continuous load de-rating rules I think there is more to it than just the avoidance of nuisance tripping.

 

[wwhitney]

210.19 Conductors — Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

Exception: If the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the branch circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

As the exception indicates, it is the limitations of the circuit breaker that require you to upsize the branch circuit conductors. If you want a normal 30A breaker to trip in a reasonable time (say 5 minutes) for a small overload (say 35A), it is difficult to achieve that in the thermal trip mechanism without also introducing the possibility that it will trip below 30A for a continuous load (say at 28A for 3 hours).

So the usual solution for a continuous load is to use a larger breaker, which now means that the circuit conductors need to have a larger ampacity to be properly protected.

Cheers, Wayne

 

[davewill]

As the exception indicates, it is the limitations of the circuit breaker that require you to upsize the branch circuit conductors. If you want a normal 30A breaker to trip in a reasonable time (say 5 minutes) for a small overload (say 35A), it is difficult to achieve that in the thermal trip mechanism without also introducing the possibility that it will trip below 30A for a continuous load (say at 28A for 3 hours).

So the usual solution for a continuous load is to use a larger breaker, which now means that the circuit conductors need to have a larger ampacity to be properly protected.

Cheers, Wayne

Thanks for the explanation. I've never really properly understood this requirement before.

 

[Valdemar]

210.19 Conductors — Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

Exception: If the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the branch circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

As the exception indicates, it is the limitations of the circuit breaker that require you to upsize the branch circuit conductors. If you want a normal 30A breaker to trip in a reasonable time (say 5 minutes) for a small overload (say 35A), it is difficult to achieve that in the thermal trip mechanism without also introducing the possibility that it will trip below 30A for a continuous load (say at 28A for 3 hours).

So the usual solution for a continuous load is to use a larger breaker, which now means that the circuit conductors need to have a larger ampacity to be properly protected.

Cheers, Wayne

Thanks for the clarification, it now makes more sense to me. However, residential breakers ARE rated for continuous current at 40C, so feeding a 30A EVSE over a #10/30A circuit is not in a direct violation with the above NEC reference. Does it mean that it is an acceptable solution if you happen to have a breaker that doesn't trip? If so, and the OP's breaker doesn't trip at 28A, does he really have to rewire with #8/40A breaker?

 

[wwhitney]

However, residential breakers ARE rated for continuous current at 40C

No, residential breakers are 80% rated for continuous current. From Underwriters Laboratory:

38. 100 Percent Continuous Rated — Unless otherwise marked for continuous use at 100 percent of its current rating, a circuit breaker is intended for use at no more than 80 percent of its rated current where in normal operation the load will continue for three hours or more

As far as I can tell, 100% rated breakers are only available in very large industrial breakers, nothing you'd see in a residence. A 100% rated breaker will be very expensive and mounted in its own enclosure, so there is no heat interaction with other breakers. For a large industrial circuit, the savings in reduced wire size can make a 100% rated breaker economical.

Cheers, Wayne

 

[MikeD]

It is interesting to note that the Siemens' VersiCharge EVSE allows for setting the maximum current output to the EV to be 6a, 7.5a, 15a, 22.5a, and 30a according to its Installation and Operations manual (http://w3.usa.siemens.com/us/internet-dms/btlv/residential/residential/docs_home/sie_im_versicharge.pdf), page 21. But on the same page of the this manual it also reads "Circuit must be sized for the max ampere requirement. Do not de-rate breakers or conductors based on amperage adjustment", i.e. even if set for outputting 6a, it requires a 40a double breaker and at least 8 AWG copper cable.

 

[Valdemar]

However, residential breakers ARE rated for continuous current at 40C

No, residential breakers are 80% rated for continuous current. From Underwriters Laboratory:

38. 100 Percent Continuous Rated — Unless otherwise marked for continuous use at 100 percent of its current rating, a circuit breaker is intended for use at no more than 80 percent of its rated current where in normal operation the load will continue for three hours or more

As far as I can tell, 100% rated breakers are only available in very large industrial breakers, nothing you'd see in a residence. A 100% rated breaker will be very expensive and mounted in its own enclosure, so there is no heat interaction with other breakers. For a large industrial circuit, the savings in reduced wire size can make a 100% rated breaker economical.

Cheers, Wayne

Well, this quote is from the Siemens circuit breaker training material:

Every circuit breaker has a continuous current rating, which is the maximum continuous current a circuit breaker is designed to carry without tripping. This rating is sometimes referred to as the ampere rating because the unit of measure is amperes, or, more simply, amps.

And this is the spec sheet which clearly states "Continuous Current Rating @ 40° C":

http://w3.usa.siemens.com/powerdistribution/us/en/speedfax-product-catalog/Documents/sf-11-sect-01-034-037.pdf

Are you saying for UL listing purposes these are further derated to 80% of the manufacturer's data?

 

[Valdemar]

It is interesting to note that the Siemens' VersiCharge EVSE allows for setting the maximum current output to the EV to be 7.5a, 15a, 22.5a, and 30a according to its Installation and Operations manual (http://w3.usa.siemens.com/us/internet-dms/btlv/residential/residential/docs_home/sie_im_versicharge.pdf), page 21. But on the same page of the this manual it also reads "Circuit must be sized for the max ampere requirement. Do not de-rate breakers or conductors based on amperage adjustment", i.e. even if set for outputting 7.5a, it requires a 40a double breaker and at least 8 AWG copper cable.

Interesting, what might be the purpose of this feature then if not installing the unit on a "weaker" circuit?

 

[wwhitney]

And this is the spec sheet which clearly states "Continuous Current Rating @ 40° C":

I am not sure why Siemens is using the word "continuous" here. I believe they mean as opposed to instantaneous trip (magnetic) or temporary overload like with motor starting. I'm pretty sure they do not mean "continuous" in the sense of the NEC term, as a load that will draw its maximum current for over 3 hours. It's rather a confusing terminology choice on Siemens part.

Regardless of what Siemens is calling them, those breakers are not 100% rated unless they meet the UL listing and are appropriately labeled. In fact, that training guide you referenced refers to 100% rated offerings, so most of those breakers are 80% rated in the sense of the UL text I mentioned earlier.

Cheers, Wayne

 

[wwhitney]

Interesting, what might be the purpose of this feature then if not installing the unit on a "weaker" circuit?

I reckon that is the purpose of the feature as per the engineer's design, and then the manual writer or lawyer got nervous and added the contradictory language.

Cheers, Wayne