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I have a 240v, 48amp (60 amp breaker, 6 awg NM-B wire) car charger outside that has a disconnect inline and last night I noticed a really weird smell in the room the wires to out to the charger from. I tracked it down using my nose to the disconnect box (or the wires leading to/from it) and at this point it was pulling 48 amps because the car was charging. I inspected the area and didn't notice any melting but since it was raining I didn't want to open the box outside to look in. I lowered the amps to 32 via the car and the smell appeared to dissipate and this morning the smell was gone. I also noticed a small humming sound from the disconnect outside at the same time.

It's a cheap disconnected: https://www.homedepot.com/p/GE-60-Amp-240-Volt-Non-Fuse-Metallic-AC-Disconnect-TFN60RCP/100674085?cm_mmc=Shopping%7CG%7CBase%7CD27E%7C27-8_CIRCUIT_PROTECT._DEVICES%7CNA%7CPLA%7c71700000034238981%7c58700003943782709%7c92700031956831784&gclid=Cj0KCQiA28nfBRCDARIsANc5BFA1htTEn9RLX9o9ot_7y6wyo4sEOySek6WKOL1FbEizxiqgrYyPfHgaAqE_EALw_wcB&gclsrc=aw.ds

But it's rated to 60 amps. Maybe something is lose, what would cause a smell/buzz? What should I check first?

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Both of the things you report - the smell and the hum - are very likely indications of a bad connection or bad contact in the disconnect.

Bad connections and bad contacts generate heat, the heat can damage the insulation of the wires, and even cause a fire.

I'd leave that disconnect off and if possible turn of the breaker for the circuit until it can be checked. You'll probably wind up having the disconnect replaced, hopefully the wiring can be re-terminated without replacing it.

  • Yeah, when it was installed I remember thinking how flimsy the screw terminals looked in that disconnect box and how I should have just paid for the extra $10 for the better one. Side question 1. Is the reason it generates heat is because there is less wire to carry the high current so more current is flowing through the wire generating heat? Side question 2: Is this why torque specs are important when connecting wires? – Ryan Detzel Nov 19 '18 at 15:51
  • @RyanDetzel - re 1. - the heat comes from the resistance in the wire; smaller wires have higher resistance than larger wires, and less surface area to dissipate the heat. Bad connections have high resistance and heat is generated at the high resistance spot, which cal lead to galling, softening the wire so it doesn't make good contact, and the connection gets even worse. re 2. - yes, the torque spec insures it's tight enough to make a good connection, given the terminals and wire and the components are all sized and rated for the load. – batsplatsterson Nov 19 '18 at 19:14
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One thing I find with larger wire sizes even though you torqued the lugs the wire is probably still loose. When I tighten larger sized wires I take them to torque specified then back off and take them down again while watching the screw position if I get more of a turn I back off and tighten again. This allows the wires to shift and get a true torque. On larger wires I grab the wires after torquing and wiggle them this allows them to move around and then re torque. I would suspect your connections are loose as this is quite common if the above steps were not taken on larger stranded wire.

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NEC Article 625.42 states that the equipment rating of an Electric Vehicle Charging System shall be rated continuous duty. So 48 x 1.25 = 60A and that is the top end of your circuit which you have installed to charge your vehicle. For me that is a little too close too maximum allowance of your circuit to make me feel comfortable with it.

Since your circuit is already installed, the best thing we can do with it is to use what is existing. I would shut off the supply breaker and then open your disconnect and look for anything that is damaged. Also it wouldn't hurt to check your connection at the breaker. Then if you need to replace the cheap (and yes it is cheap) AC disconnect and replace it with a minimum 60A standard NEMA 1 disconnect, maybe even a 100A, and maybe even a heavy duty.

If you were asking me as a contractor, I would stay with the #6 copper conductor (it is copper isn't it?). Install a 70A breaker which is allowed by NEC Article 240.6(A), and used a general duty NEMA 1 100A Disconnect at the charger. This would protect me and you of the problem you now have.

I understand if you do not want to change out your circuit, but I would also always run your charger at the 32A setting. Unless for some reason you need a quick charge. Also if you want to stay on the safe side you might invest in a infrared thermometer and check the heat output on the circuit after charging a while and see if any of the connections at the cord cap, disconnect and breaker are generating any unusual heat. Say no higher than 60C or 140F. It really wouldn't hurt to schedule a routine to check the heat output to make sure everything was operating correctly.

Stay safe and good luck.

  • Great info, thanks! I can drop the charger down to 40A, 36 or 32. Would 40 be okay for continuous use or should I drop it even further? – Ryan Detzel Nov 19 '18 at 18:22
  • 40A would be fine. – Retired Master Electrician Nov 19 '18 at 19:48
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I use the word "cheap" a lot to refer to the dreck found on Alibaba, Amazon Marketplace etc. I'm surprised to hear it associated with GE, one of the finest names in the industry. But yeah, that $7 shutoff is pretty cheap, with its plastic-bodied pull tab for a shutoff. Clearly not meant for daily use. Nonetheless, you don't have to wildly derate GE stuff like you do for cheap Cheese junk - if it says 60A it should be good for 60A (48A continuous). You can run GE equipment on the brass.*

I would shut off power at the main panel, then pull that pull-tab. If it is warped, or comes apart in your hand, then -- well, do this sometime you can afford to be without the charger for a day or two!

One thing the industry has learned through experience is that lug connections are sensitive to torque setting. Recent Code changes now require everyone to use even torque screwdrivers for the little stuff. And a lot of elecricians resent this... somehow a mechanic's beam foot-pound torque wrench is $30, but a screwdriver sized inch-pound torque wrench is $85. So some electricians (and most handymen/homeowners) just don't use torque wrenches.

Given the amount of plastic in this thing, it wouldn't surprise me if the heat was coming from a loose connection at a lug, it's making a fairly considerable amount of heat, and that is traveling up the bus bars to scorch the plastic. Thank God it's a metallic box!

It might be fixable by opening up the box, cleaning up wire ends and retorquing, and likely the torque required will be just within the working range of a mechanic's torque wrench, so ask your neighbors. However if the box is damaged, this will be your opportunity to get the better box.

Just don't confuse "more features" with "better". You don't need a circuit breaker at that location. I would say a higher ampacity would be "better".


* "On the brass" is an old 1900 era streetcar term for "to the floor". Meaning you have pushed the power controller onto the brass stop. Fair chance if you find a power controller in a museum, it'll have the familiar GE logo.

  • GE may have BEEN a fine name, but their quality has deteriorated a LOT lately, as evidenced by their being basically non-existent now. Be that as it may, this entire genre of devices, pull-out disconnects for AC units, is purposely designed to be as cheap as humanly possible, reflecting the state of the residential HVAC market. I don't care what brand you use, they are all built as cheaply as possible and are all subject to corrosion etc. 48A or not, if the connections are corroded, they will over heat. – JRaef Nov 20 '18 at 3:15
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That is also a "pull put" disconnect device, normally used for outdoor Air Conditioners. There are blades stabbing into sockets that make the connections, then there are fuse holders connected to those blades. That blade / socket / fuse clip scenario is notorious for getting corrosion that increases resistance and burns up. You get what you pay for...

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