Hot Disconnect Switch

[ddxact]

Hi,

I just wired a garage electric car charger (EVSE). The EVSE is configured for pulling 32 amp (240V) maximum, and directly connected. I am using 8-gauge copper THHN wires (2 with ground) run inside 3/4 EMT conduits about 30 feet, and then the rest with 8/2 romex in the basement for another 20 feet (total 50ft run), from the electric panel to the garage. In the electric panel I put 40 amp breaker. Somewhere in the middle of the run, I spliced the wire into an AC disconnect switch rated for 60A 240V (installed indoors, with aluminum lugs) for quick turn off of the EVSE when not in use. So far I am able to charge the car fine a few times, each charge about 6-7 hours sessions (overnight). The conduits and wires got just a little warm during use. However the AC disconnect switch gets quite much hotter, not the metal box, but the inside / plastic covers, especially during warmer ambient and humid days. One time, as soon as the charge was completed, I turned off the breaker, opened the switch, and touched the wires inside. Not burning hot, but quite hot to the touch, I'd say about 160-170F or so, almost not touchable. They look ok (not visibly burnt, yet). As far as I can tell, the lugs are quite tight. But they are aluminum, I heard aluminum heats up more than copper. Is this normal? Should I buy another disconnect switch with lugs that are made of copper (if that exist)? I am able to configure the EVSE to pull less current, let's say 24 amp, which is fine, but I'd rather be able to pull 32 amp if its ok.

Thanks for your help

 

[telectrix]

try it at 24A and see how hot it gets.

 

[ddxact]

try it at 24A and see how hot it gets.

Hi telectrix, thanks for replying.

The weather has been colder lately, and the heating at 32A is better / reduced. I did run it at 24A for a few days when ambient temp was warmer, and as such the entire circuit was pretty much cold and the disconnect switch was just slightly warm. So 24A seems to be pretty comfortable with any ambient temperature. Also about 10feet of the conduit with THHN wire is running in the attic, which could get quite hot during hot days. I guess I could switch it back and forth between 32A and 24A depending on the weather, but that is quite annoying especially with this EVSE (I have to remove the cover and adjust dip switches to change amperage limit), so for peace of mind I would probably just keep it at 24A. What do you think?

Thanks

 

[ControlsEngineer]

Just a thought--sometimes the lugs are CU only or sometimes both. You may want to check that. Could be an issue and definitely a code issue if they aren't rated for CU.

 

[ddxact]

The AC Disconnect is called Siemens WNAS2060.
It says in the panel:

60 AMP Max, non-fused
Use CU/AL wire
Aluminum terminations- To help guard against over-heating when connecting aluminum wire in CU/AL lug remove oxide film from wire and protect it with oxide inhibiting compound. Use only 60 deg. C / 75 deg. C conductors on all field installed line and load terminations.
The switch is suitable for use on a circuit capable of delivering not more than 10,000 Amperes, RMS symmetrical, 240 Volts maximum when protected by 60 Ampere maximum fuses, or a circuit breaker rated 60 Amperes maximum with a 10,000 Ampere minimum short circuit rating.

After that there are tables with wire range and lug tightening torque.

WIRE RANGE
LINE 14-8 (COPPER SOL.), 14-2 (COPPER STR.), 12-8 (ALUM SOL.), 12-2 (ALUM STR.)
LOAD 14-8 (COPPER SOL.), 14-2 (COPPER STR.), 12-8 (ALUM SOL.), 12-2 (ALUM STR.)
EQUIP. GRD 12-8 (COPPER SOL.), 12-2 (COPPER STR.), 12-8 (ALUM SOL.), 12-2 (ALUM STR.)

LUG TIGHTENING TORQUE (LB-IN)
SCREW TYPE SLOTTED
WIRE SIZE -- TORQUE
14-10 -- 32-35
8 -- 36-40
6-4 -- 41-45
3-2/0 -- 45-50

 

[Megawatt]

Hi,

I just wired a garage electric car charger (EVSE). The EVSE is configured for pulling 32 amp (240V) maximum, and directly connected. I am using 8-gauge copper THHN wires (2 with ground) run inside 3/4 EMT conduits about 30 feet, and then the rest with 8/2 romex in the basement for another 20 feet (total 50ft run), from the electric panel to the garage. In the electric panel I put 40 amp breaker. Somewhere in the middle of the run, I spliced the wire into an AC disconnect switch rated for 60A 240V (installed indoors, with aluminum lugs) for quick turn off of the EVSE when not in use. So far I am able to charge the car fine a few times, each charge about 6-7 hours sessions (overnight). The conduits and wires got just a little warm during use. However the AC disconnect switch gets quite much hotter, not the metal box, but the inside / plastic covers, especially during warmer ambient and humid days. One time, as soon as the charge was completed, I turned off the breaker, opened the switch, and touched the wires inside. Not burning hot, but quite hot to the touch, I'd say about 160-170F or so, almost not touchable. They look ok (not visibly burnt, yet). As far as I can tell, the lugs are quite tight. But they are aluminum, I heard aluminum heats up more than copper. Is this normal? Should I buy another disconnect switch with lugs that are made of copper (if that exist)? I am able to configure the EVSE to pull less current, let's say 24 amp, which is fine, but I'd rather be able to pull 32 amp if its ok.

Thanks for your help

You need to go back to the spec sheet because it sounds to me like your wire is to small. I’m guessing # 6 is the size you need. Maybe a loose connection but I doubt it.

 

[ddxact]

Hi Megawatt, thanks for the response.

I'm not a pro, so I probably missed what you mean by spec sheet. When I googled info most says that 8-gauge is good for 40 amps and 6-gauge good for 55 amps. Also note it is only at the AC Disconnect (rated at 60A) that it gets hot (which contains aluminum lugs, wires are copper), the rest of the wires are not hot like the disconnect.

Regards

You need to go back to the spec sheet because it sounds to me like your wire is to small. I’m guessing # 6 is the size you need. Maybe a loose connection but I doubt it.

 

[Megawatt]

You need to go back to the spec sheet because it sounds to me like your wire is to small. I’m guessing # 6 is the size you need. Maybe a loose connection but I doubt it.

How about taking that disconnect back and get a replacement, and use nolox on the termination screws