Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

50AMP breaker for Wall Connector is getting to 200F degrees

This site may earn commission on affiliate links.
I have a 50AMP breaker with 6/2 Romex wire (3ft run) connected to the Tesla Wall Connector and commissioned it to 50AMP breaker mode. I verified this by seeing 40AMP charging on the Model Y side. I took the breaker panel cover off and measured the temperature of the breaker with an infrared thermometer gun. The body where the lever is reads about 140F, the terminals for the Romex reads about 129F and the location near the busbar read up to 200F at one point. This is about 1 hour after charging started and the ambient temp is around 70F.

From my research 167F (75C) is typically the limit but I wonder how the breaker is surviving 200F without tripping or melting. These readings are measured after I've cleaned the contacts with electrical contact spray and retighten the lugs. I guess there's something seriously wrong with the breaker or it's 'within spec' on the busbar side? These are Square D QO breakers.
DCGw8NZVrmEyOQlYUvuvrd19-8V5UnIRenchrg2oPkDsHIv9yTvCQYp7tH7Y8WnX6CYNX9UwvPg9n2GuqcxwmxuPRRted0X0Waz5yJqyc82DvpQlXWv2XwengDWoA0Zw3IcbxKo5GOVJrLvhViLLRBWcok3VnibQX7x-KZzGhLIvTDxpn_RtL1AZC27hU9sedIXChd72_9tekRF79q432RREOCmzKZ1JPGCZGmyEQamHq_RTjgLTeirYxK6zcVcQP_jyVfiz4qeY8XiuZnrIpHtDfH0_NiZUQR3y0xiDE-f0IAWyXFH2XEGebFKsjud6oE0pLTmA0yB8CiF_KpcseG8RhpN_ZdfodhR797WjxdfFoPoT-3-H2Auxy2gXwLlQrrbf398N1SeP7xMDRufAxQjWsf3_2D_vFkpGacVSGlbcA6-gSA3JiO5-TscYtYHEpm4GcetEoATpZO4kguR2LidVtoBPEpCMEXqTF83zfJu3QMe_81M8LSD2MyjGmIhPh1b12S5rAZ_X5f4DhXCchYTlWRHL_WEHxmfXGBFnRJs8MFCv1JyniALzS-NqmLzbzLUXYuuHAkxLOJPKiNj5XodZiC0dpudRB9B6cPTRKfFNtglKr2_QxduPPwO3NhBLX0Rq9oysh4jlji3bfqzPO4j-LkrbDNzagvdt0AhIU1uG7Ywegojad6NIOgRAtGvXLFiHKPUQhXh6jrWzUaC-LH49FmgFBiA8r_rRh_9iO1I-bRDENZLunBCsN9hua0Q7nhSk_wbl6irZilztn-AAXId1XxHztceKGkhtDsCbSIhNowuOMveavwwBX4bj9fj9IAWrAMohzLNLV5codQ_6eHBQ9maMW3-0gdqQSEkTVJ459NB2eu4G_w-Lvn3ourURp841-FdjVhiE-at7QAzGOtV_UmOcRuZV8A7yIulEMuZDGrBKMw=s1329-no


IV3pjWUu03lsvJdjzvwUWNKY5MjLHaWe6JQzva2wkucN6yzZRd_FEhi_PhQIhdITlpov9w-dDoT4NjGE_1T5nqw8JzUI7V4uU-SGuBoPTZH0YXMWpMEXN0i-8WrYVgZsIfjcpJ7AY3YWGnplI64wRSE3XqjyFP56iJQUZvf5uRxZ0idlGpJHOP31FAv-LUfyXlIxH5Eg7_KWOpcxiby4Oml_m2baWqzDddXfByecNK_-8zjBvpsJygYMoGY3Hs3M541wHjrcnThagIv7RbVjXcjN1yd3WhTxVx19sXV9dTvxOjKpQBdE9bLdVmb70UKcYt76aq9HXIPuoiuzGuAf3QoeyRSvub1U4lqEp59kQQUXLVRxPrQfUhWgGDeVt9MA-3cG1CYgkSuODKPM6ul-VU1_4F3OOB6gJnadiiqjDSf64xVC5C0c5cVNkA8fU1yKJ0vmvbi4ZFNGNE_NvWyp_nsf-4T7RGzU-Bmnv92dWZuIUPuSvSaz_0_tPVxn-1t6yPlmH0CxspnuByFnlIe_7CG7Y-5H5bRimJtM5ryBpuLcIajgBFG6KiWNNNeLOvWcNRerCReboU9tKnziaksNL72Tx0UbfpUVO5PNGTQUhHrOfTKfj7bIvhtnCszd7HpQpAL2f0hrxlOBp2ObtDhKRwM_35B0EvUI5g5mb-5dx37XUcPXOAup3dTTphDUc1lAQ_LqmtI0ZWhz1odVWqzhvC73seWncbqy2n0MZLH7w764EnDha_RddHIdraHAXbacwD1FePB2k2cQf75tDiv9CGWgEz6Q03YXq8t2kDAV570aD4C9I5OkbkmgqUDyPlkg4GlRvctegVMMQhrpVtrj0LS0dQ7x9w09aepRI5sYOF_XPgKvo4b7Waere-S4-sfjK8onPgy9kcYMC8t4NGx6Qm9FOqA1emYSIEClicF8EsKavnvczg=w1770-h1329-no

RL09L3yjAipcH8echoLmNpKLg3_y0r46uk6JA7rHym_8rqA70EH7CISH2hora4r1WdkNnPkjxWgInE_hOaAys_kogHW4xh_NNq5ZytHCx3sH-omn5JQcUI8mCfp8lKvHXv8xw-Scsrkvjvz8L5jYmzVG2O4h4mWZePRnvSVxVgmreSJOErBjAMqeTMW6aRIM5hzmqmuw9JEAbk8gu_7SIKEZueOeZg3TCibgcsUPCJlRMADsWEb18bM2h7qVyG68jtMWRgAE6v2efewK1LSX7mnd50Xkme5hzYU1XOmd9B82lx9n5b8acYIOt43q5kL1NocQaIPW8NsvIlQVmT-VFMFqcsQQdCITOZKrb9XneegsLN34eSiBCeYSTsr6QNUMMVmGELKDDMxve6K064OvuKAUuHAWhYPOn4zfzfoe2F6w28Y719xGPl0wVBKlnwrZ8Cy8CyvnLHuSErRiGuNNCM4NsgcWiqGvvoGFb39AGiWUoZRAkm6n7AB7CzSgt1Sf7f6IF8hmU6EWXQciFKA__4qrQ8Tg_Lwv8BodyA_TuhRpcha_CMtpsCDOPITk4Li0r9DkiqamYgn1-VDOqNOZlgWk1zA7r7lNgwxCjTnn250Fc01-eFdUo1FAf-Iojkdozr1u3jQS4boEQzLAe9Kr7ffC6LLkFM4w_NFWakb7WjLjdxjdlFEiY1bCIoSVAa74YypbQGKANF3TLoL3COVSIKLFqLV1O2q6RJ-qY3pweOY7JvgikaCM-6lZVfX_11VUuwijGak0Y5_5ZWDKZ5IpWyQAY4w_S8xBn_N4fXBTbY1IxqoiF9Oo_Z6WbC0oly3MQfJovR3r5W_2xdyCx40DO3Lo_H4_l9fQ88N1PXJ53RMZ0bZ85rMSllROBEIQfvzehyhxVHJYWXkRFL7lRUVjDiw3iknvsXK6PNdRnQ7rqKEjgo8-hw=w997-h1329-no
 
  • Informative
Reactions: zoomer0056
Your pictures don't work for me.

I suspect a slightly loose terminal and/or a faulty breaker. After a little over 2 years, my receptacle melted from a terminal that has loosened itself from all the heat cycling. I replaced it, and a short while later the breaker tripped during charging. I checked and it was too hot to touch. I retightened the terminals and put it back and now it's just barely warm. The terminals weren't obviously loose, but I was able to tighten them just a tiny bit. Apparently it doesn't take much.

I originally charged at 40A (50A breaker, 6/3) but now I charge at 32A unless I need to top off quickly.
 
Just as a datapoint, my HPWC is drawing 48A(yes, not 40) on a 50A breaker (cutler-hammer CH250), using #6 romex in my ~65f basement. After three+ hours, in free air 20 feet from my panel, the romex is 90f. The face of the breaker is 100f in the nearby utility room with a ~55f room temperature, all far far below even the 140f(60C) of romex.

I'd agree that there's something dreadful wrong with your breaker.
 
  • Helpful
Reactions: pilotSteve
Yes, he's a long timer here, and has been told that the 6 gauge Romex being used as a 60A circuit is violating code, and it's his knowing decision to continue using it that way.
Per NEC Table 310.15(B)(1), ambient temp 60-68F, I'm allowed to uprate my 60C conductor by 15%, so 55*1.15=63.25A is the temperature adjusted rating for my #6 NMB.

It therefore isn't a code violation to use it for as much as 50.6A (63.25*0.8)
 
  • Disagree
Reactions: Rocky_H
Per NEC Table 310.15(B)(1), ambient temp 60-68F, I'm allowed to uprate my 60C conductor by 15%, so 55*1.15=63.25A is the temperature adjusted rating for my #6 NMB.

It therefore isn't a code violation to use it for as much as 50.6A (63.25*0.8)
Sorry but that is all incorrect. You can't uprate it AT ALL above the 60 degree C temperature rating. The section on temperature DErating (notice how it's de- and not up-?) says you can start with the 90 degree C column for the insulation of that wiring and start reducing it down from there. If it takes you down below what the 60 degree column is, then yes, you have to use the lower value. But it says if the calculations yield a number that is above the amps shown for the standard NM-B 60 degree column, then you just have to default back down to the 60 degree column--you can't go over that at all.
 
  • Informative
Reactions: zoomer0056
Sorry but that is all incorrect. You can't uprate it AT ALL above the 60 degree C temperature rating. The section on temperature DErating (notice how it's de- and not up-?) says you can start with the 90 degree C column for the insulation of that wiring and start reducing it down from there. If it takes you down below what the 60 degree column is, then yes, you have to use the lower value. But it says if the calculations yield a number that is above the amps shown for the standard NM-B 60 degree column, then you just have to default back down to the 60 degree column--you can't go over that at all.
See page 3... "For ambient temperatures other than 30°C (86°F), multiply the ampacities specified in the
ampacity tables by the appropriate correction factor shown below."


Multiplying by 1.15 sure sounds like not DErating to me. Sadly, most of the tables I've seen only have the higher DErating temperatures listed.

Lets just say if I mysteriously disappear from the forum, it probably WON'T be because my #6 Romex that consistently runs at 90F in my basement suddenly decided to jump to 170F.
 
See page 3... "For ambient temperatures other than 30°C (86°F), multiply the ampacities specified in the
ampacity tables by the appropriate correction factor shown below."

https://www.nfpa.org/~/media/Files/Code%20or%20topic%20fact%20sheets/NECAmpacityWorkflow.pdf
Multiplying by 1.15 sure sounds like not DErating to me. Sadly, most of the tables I've seen only have the higher DErating temperatures listed.
This is why I don't envy code inspectors. NEC is very large, and for people unfamiliar, they may find a section like this, and think they have the whole story, because they did not know about a different section that specifies a condition further. Fortunately this is in very plain wording that shows why you can't overclock your wiring like that.

That's near the bottom of page 7 of that 8 page document that they show the quoted text of NEC 334.80.

This is section 334.80 "Ampacity"

"The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall
be in accordance with the 60°C (140°F) conductor temperature rating. The 90°C (194°F) rating shall be permitted to
be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60°C (140°F)
rated conductor"

See that last specific part? The calculated value cannot exceed the 60 degree C value.
 
Last edited:
"The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall
be in accordance with the 60°C (140°F) conductor temperature rating. The 90°C (194°F) rating shall be permitted to
be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60°C (140°F)
rated conductor"

See that last specific part? The calculated value cannot exceed the 60 degree C value.
I stand corrected.
 
And sorry if I'm sounding rude or confrontational. It's just one of those things where if it has a specific correct answer, I get kind of stuck on not wanting to leave misunderstandings out there about it.
It's all good. I'd much rather be corrected when I'm wrong than continue to repeat incorrectness.