NEMA14-50: How much current can you pull?

TEG · May 28, 2009

The topic of the NEMA14-50 socket has come up a lot lately.

When seeing one, someone might want to assume that they could get 50amps of current out of one. For instance, check these specs/features:

Leviton 125/250V Flush Mount Receptacle - Industrial Plugs - Leviton 279 - LevitonProducts.com

Features:

50Amp

125/250V

3P, 4W

Straight blade

Industrial grade

Self grounding

Side wired

Steel strap

NEMA 14-50R

So that "50 Amp" feature can be misleading. I think that describes the max capability of the physical connector, but current can be more limited by the equipment behind it. For instance, there could be a 40 or 50 amp breaker. If a 40 amp breaker, code says you shouldn't draw more than 32 amps. If a 50 amp breaker, code says no more than 40 amps.

This page says:

...50A NEMA 14-50 S supplied by 40A service Current NEC code prohibits this configuration allthough many cities have not enacted current NEC code into law yet...

So, I think there are some NEMA 14-50 with 40 amp breaker installed out there.

Also, various adapters may provide a NEMA 14-50 even though there is a smaller than 50 amp breaker behind it.

For instance, this Y cable is called "MAXIMIZER RV 50-AMP GENERATOR ADAPTER" yet it provides far less than 50 amps of capability.

Various cable adapters, like those from EVnut will also let you plug NEMA14-50 equipment into 30 amp sockets.

Also, the EAA Avcon to NEMA14-50 adapter box mentioned on the EVnut site above lets you get a NEMA14-50 socket that has equipment behind it that typically only pulls about 25 amps, not 50.

The Tesla MC240 is listed as "30 amp capable", and some have wondered "why not 40" or "even 50", and I think the above illustrates why it is safer for it to not use more than 30. Some home made kits have been able to adapt Avcon to Roadster without using the MC240, but one needs to be careful about how much current you try to pull through the Avcon cable. 25 amps is probably most appropriate. 30 or 32 amps is pushing it. 40 amps is probably too much.

If you have a home installed NEMA14-50 not adapted from another socket, and you know it has a 50 amp breaker, and suitable wiring gauge, then yes, 40 amps can work, but if on the road at an unfamiliar NEMA14-50 or Avcon it is probably best to stick to lower current.

TEG · May 28, 2009

I wonder how hard it would be to change the MC240 to have a pilot signal that lets it pull 40amps rather than 30. I think that is one thing some people want, and have turned elsewhere to find. The < 30amps is safer, but if you absolutely know your circuit you might want a little more.

donauker · May 28, 2009

TEG said:
I wonder how hard it would be to change the MC240 to have a pilot signal that lets it pull 40amps rather than 30. I think that is one thing some people want, and have turned elsewhere to find. The < 30amps is safer, but if you absolutely know your circuit you might want a little more.

A 40 amp pilot signal could be generated rather easily. I am not sure if the current signal generator could be readily altered, I have not yet dug that deep. The limitation is that the current GFI device being used is only 30 amps.

TEG · May 28, 2009

Another mod idea would be to put a NEMA 10-30 on the existing EAA Avcon boxes so that Martin's cable set uses the cable that causes a 24amp pilot signal to be sent. Then no chance of tripping the Avcon EVSE overcurrent, or need to change VDS settings.

donauker · May 29, 2009

TEG said:
Also, various adapters may provide a NEMA 14-50 even though there is a smaller than 50 amp breaker behind it.

For instance, this Y cable lets you plug into 30 amp and 15 amp circuits and create a NEMA 14-50 socket which purports to have 45 amps of circuit breaker behind it.

This device is very misleading in that it combines a 30 amp 120 volt circuit with a 15 amp 120 volt circuit. This device will only provide 15 amps at 240 volt.

Tdave · May 29, 2009

The MC240 draws 30 amps only because there are no 40 amp GFCIs for Tesla to use. So they use a 30 amp GFCI and limit draw to 30 amps. Once they can source a 40 amp GFCI, the MC240 will be upgraded to 40 amps.

TEG · May 29, 2009

donauker said:
This device is very misleading in that it combines a 30 amp 120 volt circuit with a 15 amp 120 volt circuit. This device will only provide 15 amps at 240 volt.

Yipes. So even though it could hook to an MC240, or Roadster Foundry kit you can't even get anywhere near 30 or 40 amps from it.

I started a whole new topic just to discuss campground charging and those odd 'cheater' cables.

TEG · May 30, 2009

By the way, here was one of the sites advocating the home brew EVs use Avcon.

Currently, conversion EVs should seriously consider using the Avcon conductive connector. It's quite robust, a standard that is shared with production EVs and there are numerous charging stations in CA and AZ. It complies with current electrical code, specifically NEC Article 625. It costs a bit more than a NEMA 14-50 but the difference is not significant for a public charging station installation. It's a bit more significant though reasonable for a home self installation. If you're paying for someone to install, you should go with the Avcon. The NEMA 14-50 violate National Electrical Code when used for Electric Vehicle recharging.

EVnut · May 30, 2009

TEG said:
So that "50 Amp" feature can be misleading. I think that describes the max capability of the physical connector, but current can be more limited by the equipment behind it. For instance, there could be a 40 or 50 amp breaker. If a 40 amp breaker, code says you shouldn't draw more than 32 amps. If a 50 amp breaker, code says no more than 40 amps.

This is true of any outlet, of course. I'm not sure why the 14-50 is being singled out. I can put a 20A breaker behind an L6-30, and have the same problem. I can use 18 gauge wire behind a 120V 20A outlet and have the same problem. The 50A capacity is the capacity of this connector. That is all it means. If it is wired incorrectly, then it is wired incorrectly. That doesn't mean that the designation is somehow misleading. The designation only means that you should neve use the outlet to pass more than 50A. What else would it more accurately be called?

folsomev · May 30, 2009

TEG said:
Another mod idea would be to put a NEMA 10-30 on the existing EAA Avcon boxes so that Martin's cable set uses the cable that causes a 24amp pilot signal to be sent. Then no chance of tripping the Avcon EVSE overcurrent, or need to change VDS settings.

Unfortunately, Martin's cable set does not have a 30A or 32A setting. That's a drawback.

folsomev · May 30, 2009

Originally Posted by TEG
So that "50 Amp" feature can be misleading. I think that describes the max capability of the physical connector, but current can be more limited by the equipment behind it. For instance, there could be a 40 or 50 amp breaker. If a 40 amp breaker, code says you shouldn't draw more than 32 amps. If a 50 amp breaker, code says no more than 40 amps.

EVnut said:
This is true of any outlet, of course. I'm not sure why the 14-50 is being singled out. I can put a 20A breaker behind an L6-30, and have the same problem. I can use 18 gauge wire behind a 120V 20A outlet and have the same problem. The 50A capacity is the capacity of this connector. That is all it means. If it is wired incorrectly, then it is wired incorrectly. That doesn't mean that the designation is somehow misleading. The designation only means that you should neve use the outlet to pass more than 50A. What else would it more accurately be called?

There are no NEMA 40A outlets. I don't find anything in the Code that prohibits installting a 14-50 receptacle on a 40A circuit. It's fairly common.

It's OK to install a 15A receptacle on a 20A circuit, but it is not OK to install a 20A receptacle on a 15A circuit.

The 80% rule applies only to continuous loads, but EVs are indeed considered continuous loads. The 14-50 is not an EV connector. If on a properly wired 50A circuit, it can handle 50A for shorter periods, so there is nothing wrong with the specifications describing it. If you don't know what the circuit configuration is, it would be best for an EV not to draw more than 32A. If you know it is on a proper 50A circuit, then 40A would be fine. For the Avcon adapter box, 32A is ok under most circumstances -- always if the Avcon box is an ICS-200.

Of course, 70A from a Tesla HPC on a 90A circuit is even better than any of the above.

folsomev · May 30, 2009

TEG said:
By the way, here was one of the sites advocating the home brew EVs use Avcon.

This site is from 1997. Not entirely relevant today.

TEG · May 30, 2009

folsomev said:
This site is from 1997. Not entirely relevant today.

I think it was a little more recent than that (but how can you tell)? It talks of the 1999+ RAV4 EV there, so it seems like it was authored after 1997.

Is there something similar with more up to date information you recommend we reference instead?

folsomev · May 31, 2009

folsomev said:
Unfortunately, Martin's cable set does not have a 30A or 32A setting. That's a drawback.

TEG said:
I think it was a little more recent than that (but how can you tell)? It talks of the 1999+ RAV4 EV there, so it seems like it was authored after 1997.

Is there something similar with more up to date information you recommend we reference instead?

If you view source, you will see the following comment:


No, there is nothing more current. The SAE J1772-2009 connector is overdue. It should have been available for initial Tesla production. The delay is causing several problems.

Vger · Jun 2, 2009

For those who want to learn more about the various NEMA receptacle types and their approved and intended uses, see here: NEMA connector - Wikipedia, the free encyclopedia

TEG · Jun 7, 2009

EVnut said:
This is true of any outlet, of course. I'm not sure why the 14-50 is being singled out....

I have been making a big deal about the 14-50 for a few reasons:

#1: Tesla's only portable 240V charge cable (MC240) uses it it.
#2: The "Roadster Foundry" NEMA14-50 cable set is currently set to draw 40 amps by default when you use NEMA14-50.
#3: NEMA14-50 is the RV campground standard for "50 amps".
(When a campground says they "have 50 amps" it means they have NEMA14-50).

Please see the new Campground Charging topic where I mention the various "cheater" and "dog bone" adapters that RV shops will sell. I want to make sure that Roadster drivers don't head to a campground and plug their Roadster NEMA14-50 (either MC240 or Roadster Foundry) kit into one of these adapters that claims to be "50 amps" (but really isn't), or 240V (but really isn't). Someone could get stuck at a campground, out of charge, thinking they had cables needed to charge but finding out it doesn't work.

I also wanted to make sure that Roadster owners were aware that the "Roadster Foundry" kit NEMA14-50 -> EAA Avcon box could overload the Avcon EVSE circuit.

You probably know all of this already, but I wanted to get the discussion down online so that those new to the EV charging world have a better understanding of what is going on here.

vfx · Jun 7, 2009

TEG said:
I have been making a big deal about the 14-50 for a few reasons:... I wanted to get the discussion down online so that those new to the EV charging world have a better understanding of what is going on here.

I for one appreciate the clarity and will reference these threads often.

ChargeIt! · Jun 7, 2009

vfx said:
I for one appreciate the clarity and will reference these threads often.

YES !!! THANK YOU, TEG ! :smile:

Tdave · Jun 7, 2009

folsomev said:
Unfortunately, Martin's cable set does not have a 30A or 32A setting. That's a drawback.

It doesn't matter. The car does have those settings. So you you set the car to draw only what the outlet and the breaker behind it supports.

TEG · Jun 7, 2009

ChargeIt! said:
YES !!! THANK YOU, TEG ! :smile:

Thanks for the feedback. I was starting to wonder if my writings were well received or not. I don't know how much of this kind of thing has been discussed on the owners forum already.

NEMA14-50: How much current can you pull?

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