Anyone use this Romex 6/3 cable during install?

[MY-Y]

Before the wire gets potentially hot enough to start a fire, wouldn't the car notice a voltage drop and automatically lower the amps? I have to think Tesla thought of this and if not, there would be a lot of fires.

I agree 100% with following the code and being safe and I would never trust voltage drop sensing vs. proper wiring, but I'm curious if anyone here knows whether the car does this or not.

Keep in mind that we are mixing "code" and "safe." Code covers many scenarios (wire in a well insulated wall, house in a very hot climate, etc.) There is margin built in for safety. A 60 amp draw on a 6 gauge romex is 9% over its rating. This means ~19% more heat in the wire. Is this to code? No. Is this safe? That's a different debate. Since the vast majority of the members here aren't qualified to judge electrical safety, I think it's best to keep to code.

As far as the car preventing a fire by noting the voltage drop, that is not something I'd rely on. It will happily charge at 48 amps with a 5 volt drop. That's 240 watts being dissipated in the system. If that heat is spread out across a long wire, no big deal. If that heat is in a small area, it is more than enough to light a fire. A 30 watt soldering iron can easily start a fire.

Edit: I just noticed that Johnny Vector covered some of this while I was typing my reply.

 

[Midnightsun]

Don't assume those are the same. I was talking a bit in private messaging with an electrician who is in Canada, and NMD90 is just something different that Canada has, and it must be a little bit different in why it's allowed some different amp ratings at different temperatures.

NMD90 is simply Non Metallic Dry locations rated for 90 degrees C
NM-B is simply Non Metallic and the b stands for a rating of 90 degrees C, NM-B is designed for Dry locations

Both have the same type jacket and insulation and 6 gauge copper is 6 gauge copper so what is the difference if they are not the same? Personally I cannot see any difference in the specs except that the NM-B is not CSA certified therefor not acceptable in Canada and visa versa for the NMD90

 

[MY-Y]

NMD90 is simply Non Metallic Dry locations rated for 90 degrees C
NM-B is simply Non Metallic and the b stands for a rating of 90 degrees C, NM-B is designed for Dry locations

Both have the same type jacket and insulation and 6 gauge copper is 6 gauge copper so what is the difference if they are not the same? Personally I cannot see any difference in the specs except that the NM-B is not CSA certified therefor not acceptable in Canada and visa versa for the NMD90

NM-B is rated for 60C in the USA, not 90C.
Although it is rated at a 90C conductor temp, its ampacity is limited to 60°C according to the NEC. From what I read, the 90C is for derating calculations, fixture terminations, etc. Regardless of that, when all of the calculations are done, you cannot exceed the 60C ampacity rating.

For our Tesla HPWC to operate at its 48 amp max, it's simple. 60A breaker on a 4 gauge 60C wire (e.g. NM-B) or 6 gauge 90C wire (e.g. THHN in conduit, MC). No need to over complicate it or push the limits with a high current circuit.

 

[sleepydoc]

A couple of observations -
First, if the wire is exposed you may be required to protect it in conduit. Code requires it to be protected ‘where subject to damage.’ This is a bit open to interpretation by the inspector.
Second - if you have questions, call your local electrical inspector and pull a permit. It’s a small price to help ensure you’re wiring things correctly.
Finally, if you really have to ask this many questions, you probably shouldn’t be doing the wiring yourself anyway.

 

[Magnetic Flux]

NMD90 is simply Non Metallic Dry locations rated for 90 degrees C
NM-B is simply Non Metallic and the b stands for a rating of 90 degrees C, NM-B is designed for Dry locations

Both have the same type jacket and insulation and 6 gauge copper is 6 gauge copper so what is the difference if they are not the same? Personally I cannot see any difference in the specs except that the NM-B is not CSA certified therefor not acceptable in Canada and visa versa for the NMD90

If I were a betting man I would bet that Southwire (manufacturer of Romex) likely makes the exact same cable for CSA certified NMD90 and NEC listed NM-B due to the simplicity of manufacturing massive quantities of these cables. Simply having to print a different lettering on the outer jacket is much simpler from a manufacturing perspective.

In the end, we have the follow the code requirements in the regions we live, so in the US we need to follow the requirement that all NM cable is only rated for 60 deg C.

I would also venture to say that most people installing these feeds into their garage probably aren't following the temperature derating of the conductors to begin with and probably are not checking the limitation and listing on the terminations in the panelboard or at the wiring device. With that, I would err on larger size conductors (or better rated ones).

The other thing to remember in the US is that the National Electrical Code (NEC, also known as NFPA 70) is part of the National Fire Protection Association books of standards and codes. It isn't a standalone code like the Mechanical Code and Plumbing codes, etc. The NFPA documents focus on life safety and human protection. I was taught years ago to think of the NEC as being developed for life safety, above all else. It helps explain a lot of the requirements and decisions made.

 

[Midnightsun]

Not saying one should not follow code to the contrary as originally stated and obey the laws where one may live after all the code is kind of like the electrical law. Just curious as to why the rather large acceptable ampacity of the 2 standards differ so much yet seem to be identical in fabrication.

My brother lives in NH, and I have a condo in Florida. Oddly enough I can go to any of these locations and ride my motorcycle with no helmet. Heck in NH an adult is not even required to wear a seatbelt. Safety first, LOL. There are quite a few items in Canada that are not to code yet are in the states and in fact you cannot even buy them here such as those plastic remodelling boxes which I personally think are the best thing since sliced bread. Considered unsafe here yet not in the US, go figure.

 

[JeffnReno]

Thanks for all the input.

I'm a little confused, it's true that the wire I linked to only has a max 55 amp rating, but the Tesla wall charger data shows the
Maximum output (amps) of 48 amps on a 60 amp breaker. If the max output is only 48amps for the charger, can't I use the 55amp cable?

Now that I think about it, it's probably a bad idea because a future owner of this house might add a different charger and calculate it off the breaker and not the cable which might not end well.

Since the garage has unfinished walls I would rather not run conduit but use a jacketed cable for easier install.

Just use a 50amp breaker. I ran mine to a 14-50 outlet which is rated for 50amps anyway and I use my mobile charger that came with my car which only charges at 32amps and is plenty for overnight charging.

 

[dn325ci]

I understood all this, and found it informative as a newbie. A question I didn't really see brought up here: what role does the length of the conductor play? Seems like long runs would make this problem worse. When talking about 6/3 or any other conductor, it made me curious what length of line was assumed in the standards setting.

 

[Rocky_H]

I understood all this, and found it informative as a newbie. A question I didn't really see brought up here: what role does the length of the conductor play? Seems like long runs would make this problem worse. When talking about 6/3 or any other conductor, it made me curious what length of line was assumed in the standards setting.

Ah, that's a good question. Extra length in the line mainly causes an issue with voltage drop by the time you get to the end of the line. That's generally not a danger issue as much as an effectiveness issue. Some kinds of devices have problems if they are not getting voltage as high as they are expecting. Fortunately with charging an electric car, that's not really much of an issue. They usually have really wide tolerance to detect and use whatever lower levels they are getting, so some sagging by several volts isn't going to matter.

Electric code doesn't have strict rules on that either; they have more of recommendations of trying to keep the voltage drop to within reasonable % and upsize the wire thickness if necessary to compensate. For regular house installations, where the runs are usually less than 100 feet, it's probably not an issue you need to consider. It's more of commercial settings, where they might have to run something a few hundred feet out to some charging stations in the parking lot that they would need to take that into account.

If you want to experiment with this some, here is a voltage drop calculator tool. You can either see what wire requirements you need to stay tight within a certain % drop, or you can loosen up the drop % and just see how much drop there is over that length. And you can play around with the variables to see what it gives for different lengths and wire gauges.

Voltage Drop Calculator | Southwire US

www.southwire.com

And one other thing. Tesla did build in a little software check into the car that will compare the voltage before charging to after it ramps up and pulls heavy current, and if that shows a sizeable drop, it will show a warning and try a lower current level. So if there is a really long run or with undersized wire, the car may detect that. But those usually don't flag there, because it's looking for the change, and a long circuit is probably already a bit low voltage to start with. But it's more as a safety check, because if there is a loose connection, even on a very short run, that weak spot is very resistive and will have a big voltage drop when current tries to go through it, which can be a hot spot and dangerous.

 

[qdeathstar]

No, no, NO! And this is where we see how people keep getting this wrong over and over and over again (even electricians sometimes). Thank you, @bmil03 for linking to that other thread, but this was already discussed and corrected in this thread on the previous page!!

People have heard about that "next size up" rule, and they make this giant incorrect leap to the conclusion that a magic wand has now been waved that makes the whole thing, end to end, a full, legitimate 60A circuit. That is FALSE! It's still limited by the wire as a 55A circuit.

You can still put a 60 amp breaker on 6/3 nm cable. You just can’t pull 48 amps from the circuit.

 

[MN-MS100D]

You can still put a 60 amp breaker on 6/3 nm cable. You just can’t pull 48 amps from the circuit.

Wrong. Conductor and breaker must be 125% of continuous EVSE load. 50A breaker max. 625.41

 

[qdeathstar]

Wrong. Conductor and breaker must be 125% of continuous EVSE load. 50A breaker max. 625.41

Wrong. It is fine to put 6-3 nm on a 60 amp breaker. It is stated in the code.

You need to make sure your continuous load is less than 44 amps.

 

[Rocky_H]

You can still put a 60 amp breaker on 6/3 nm cable. You just can’t pull 48 amps from the circuit.

Wrong. It is fine to put 6-3 nm on a 60 amp breaker. It is stated in the code.

You need to make sure your continuous load is less than 44 amps.

You are being pretty annoying and misleading people. Please stop. I know this is all very nitty gritty, technically correct at the minutia level, but it is going to lead people to do installs wrong a lot, and there is no good reason to tell that to people. It is just not a good idea to use a 60A breaker with that, so please stop advising it.

 

[qdeathstar]

You are being pretty annoying and misleading people. Please stop. I know this is all very nitty gritty, technically correct at the minutia level, but it is going to lead people to do installs wrong a lot, and there is no good reason to tell that to people. It is just not a good idea to use a 60A breaker with that, so please stop advising it.

What you said was wrong. Be accurate.

As far as very nifty gritty, that is why you hire professionals. There is nothing wrong with installing 6-2 nm cable on a 60 amp breaker. It is routinely done with air handlers and the like. You are falsely creating a generalization that doesn’t exist.


The over current protection device has little to do with wire size. In fact, there are some instances where it is perfectly permissible to install a 100 amp breaker on six awg wire.

http://nationalequipmentsolutions.com/wp-content/uploads/WQ-Electric-wire-chart_001.pdf

It is important to be accurate.

If you put a charger that draws 48 amps on a 50 amp circuit breaker, the install would still be wrong. Telling people to “put it on a 50” is useless. Not to mention potentially more dangerous.

 

[Rocky_H]

What you said was wrong. Be accurate.

It is important to be accurate.

Yes, it absolutely is important, so you'd better give a citation for your accusation about me. Quote what I said that you think is wrong, and we'll discuss it instead of your B.S. vague accusations. You've been on a weird quest to give people dangerous, misleading advice on this topic for a very long time.

 

[qdeathstar]

Yes, it absolutely is important, so you'd better give a citation for your accusation about me. Quote what I said that you think is wrong, and we'll discuss it instead of your B.S. vague accusations. You've been on a weird quest to give people dangerous, misleading advice on this topic for a very long time.

Can you quote where I gave anyone advice?

 

[Rocky_H]

Can you quote where I gave anyone advice?

You can still put a 60 amp breaker on 6/3 nm cable. You just can’t pull 48 amps from the circuit.

It is fine to put 6-3 nm on a 60 amp breaker. It is stated in the code.

You are telling people they can put a 60A breaker with 6 gauge Romex on their home charging installations multiple times.
What are they supposed to do with that?
They wouldn't be allowed to put a 60A outlet on it. They wouldn't be allowed to put a 50A outlet on it. They wouldn't be allowed to put a Tesla wall connector on it, because there is not a 55A circuit setting. All they can have is a set of bare wires, because there's nothing code compliant they can do with that. So by your telling people to use a 60A breaker, they are going to attach something wrong on the other end that is dangerous. You are being negligent and irresponsible in doing this just to try to score some kind of attitude points.

I have already gone through this in detail about how there is a very small window of technicality to using that wire with a 60A breaker on it, but there is nothing that can be properly set up for that on the other end for EV charging, so you need to stop telling people that it is OK to do.

And again, I am asking you to give the citation for the false accusation you made against me.

 

[qdeathstar]

You are telling people they can put a 60A breaker with 6 gauge Romex

yes I am, that is true.

on their home charging installations multiple times.

no I am not. But it would be true if they turned down the current setting to below 44 amps.

What are they supposed to do with that?
They wouldn't be allowed to put a 60A outlet on it. They wouldn't be allowed to put a 50A outlet on it. They wouldn't be allowed to put a Tesla wall connector on it, because there is not a 55A circuit setting.

If there was a 55 amp setting, that would be wrong.

I have already gone through this in detail about how there is a very small window of technicality to using that wire with a 60A breaker on it, but there is nothing that can be properly set up for that on the other end for EV charging, so you need to stop telling people that it is OK to do.

it is because you are missing the point. The reason that 6-2 NM isn’t suitable for a car charger at 48 amps has nothing to do with the over current protection device.

So your point that 6-2 NM can’t be installed on a 60 amp breaker is 1) wrong and 2) irrelevant.

And again, I am asking you to give the citation for the false accusation you made against me.

What accusation?

 

[LEBSD]

I assume that your going to buy the Power Wall Charger? Remember, the normal mobile charger will only go up to 32 Amps/240V (learned that after installing a 50Amp breaker/wiring). As others stated above, you need #4 NMB (rated max 70Amp). Also, NMB can not be exposed and it cannot be in a conduit. I recommend using PVC Electrical pipe and run 2 #4 (240V), your gnd does not need to be a #4, can be smaller.

 

[DonaldBecker]

I assume that your going to buy the Power Wall Charger? Remember, the normal mobile charger will only go up to 32 Amps/240V (learned that after installing a 50Amp breaker/wiring). As others stated above, you need #4 NMB (rated max 70Amp). Also, NMB can not be exposed and it cannot be in a conduit. I recommend using PVC Electrical pipe and run 2 #4 (240V), your gnd does not need to be a #4, can be smaller.

A reminder to readers that "cannot be in a conduit" isn't as simple as it sounds.
NM-B can be "sleeved" for protection. Which means running the exposed part in a conduit, and not calling it a conduit.

There are extensive discussions elsewhere on the rules and interpretation. The take-away is that NM-B in 'conduit' isn't always a code violation. The most common place to see it is in a garage, just where you would find an EVSE connection.