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When I went to add a light switch near my attic access for an existing light with a pull cord, I found that the light was wired to the disconnect box that feeds the air handler. This particular circuit is fed by a 60A breaker in my main panel (I assume it is so large due to the emergency heater if the heat pump is not working).

The light is wired with a 10 gauge cable, but this just seems really wrong to me. I suspect this was put in by the AC guys before we owned it since it was attached to a truss with hex head screws. It also didn't even have a junction box! The fixture was directly attached to the truss with enough clearance to wire it from the back. The terminals were exposed to open air and someone could have have touched a live 60A circuit. These are the same AC guys that cut 3 truss members so I don't have a lot of faith in what they did.

I have fixed the junction box situation, but before I add a switch to this I wanted to confirm that I need to move this to another circuit. Maybe there is another breaker inside the disconnect box that is only 15/20A? I didn't see anything...

This light fixture also has a receptacle built into it. Like this: Light with Outlet

Update

I looked a little further into it and the neutral for the light is connected to the ground and it measures 120V at the receptacle. There is what looks like a 2 gauge aluminum coming in and a 6 gauge aluminum going out to the heater/ air handler, plus the 10 gauge copper going to the light/ receptacle. There is no separate 15A for the air handler. Side note, why does the tester show hot/ground reversed for this situation? My pictures don't stay rotated properly on the phone app...

Overview

Connections

Tester

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    Currently this would be a code violation. Installing a proper breaker and wire would be the correct and safe way to power the light. – Ed Beal Jan 30 '17 at 19:20
  • @EdBeal is the reason this is a code violation that this is a 15A receptacle on a 60A circuit? – brhans Jan 30 '17 at 20:42
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    @brhans search NEC for the exact string "15 or 20" and you'll hit the relevant code section immediately. You can only install 15A receptacles on 15A or 20A circuits. This is a 60A circuit. – Harper - Reinstate Monica Jan 30 '17 at 23:00
  • @Harper also, can't you only install the 1 fixture on a 60A circuit? So even if the receptacle were 60A, it wouldn't be allowed on the same circuit as the HVAC? – mmathis Jan 30 '17 at 23:20
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    @mmathis Can't use 240V for lighting in residences. Can't put 120V loads on a 60A aux heater circuit. Good luck finding a 60A receptacle, and can't put one on a circuit whose fixed load is >50% of capacity. Generally things over 30A are one machine per circuit, where multiple they are all the same item e.g. Heaters. – Harper - Reinstate Monica Jan 30 '17 at 23:28
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This is an unmitigated disaster

Firstly, 60A auxiliary heater circuits are normal enough, but they don't have neutral. The wires are L1-L2-ground or black-red-bare. There is no way to get 120V out of that circuit, except by bootlegging neutral.

Bootlegging neutrl means misusing ground as neutral, intentionally connecting a "hot" wire (via a light bulb or tool) to the ground. If the ground-neutral bond in your panel has any sort of problem, it will electrify every ground in your house. Bad idea.

Nothing prevents someone from plugging in a power strip and four 1500W heaters. That will overheat the wiring and start a fire.

This is terrible work!

Must be more going on

Thing with heat pumps is there are usually other circuits involved. I am surprised that the air handler would share the 60A aux heat circuit, I would expect there to be a 15-20A circuit there for the air handler. I would think it might also be 120V. If so, it may be possible to borrow it for the attic light. The attic light must be on a 15 or 20A 120V circuit. It cannot use part of a 120/240 circuit.

The total of all hard-wired loads on a circuit must be less than 80% of total circuit capacity.

You cannot have any receptacles on a circuit unless the hard-wired loads are less than 50% of total circuit capacity. So you may need to change lamp fixtures.

Or, go 24V lighting

In this day and age, LEDs are so efficient that 5W of lighting is a fair bit, and two would light up an attic decently enough. Most furnaces have a 24 volt AC, 40VA (similar to watts) transformer with surplus capacity. You could grab 24VAC off the transformer and take it to LED lights. You would need to find LED fixtures that have no replaceable bulb, and work a range of voltages including 24V AC. You can use common thermostat wire to hook them up. Aim for an even number of lights, and hook each one reverse polarity of the next. Sometimes LEDs will tolerate AC but only light on half the AC cycle, by reversing polarity to every other one, you assure the full cycle is used.

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  • Normal LED strips that are 24V really shouldn't be used back-to-back on AC because the peak-to-peak voltage will get higher than 24V, causing about 150% of the nominal current to flow through the LED. It's a great way to turn an LED into an incandescent (I've done it). Also, the LEDs might breakdown at the large reverse voltage applied to them, causing another potential over-current situation. Safest bet is a rectifier with a switching regulator. – Hari Ganti Jan 31 '17 at 0:22
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    Most manufactured LED fixtures have a switching constant-current power supply which accepts a range of voltage, e.g. 11-36V. That is the type to use, though, they won't necessarily make good use of an AC input. To get best brightness out of expensive emitters, current must be controlled precisely, and that requires an active circuit. Passive (resistors) forces you to derate the emitter so much that you spend more on emitter overkill than you save avoiding an active power supply. – Harper - Reinstate Monica Jan 31 '17 at 1:11
  • Thanks for all the information. I didn't even think of the 240V issue, I guess that CFL bulb has been able to cope with it so far... If anyone ever used the receptacle I guess they were feeding their tools 240V! I'll try to get up there tonight and see if there is another 120V circuit for the air handler, but if there was you'd think the HVAC guys would have used that (because it would be easier/cheaper, not because they were smart). – jmpreiks Jan 31 '17 at 14:11
  • @jmpreiks they were getting 120V for the socket by connecting to one of the hots, and to ground, sp bootlegging a neutral. – Harper - Reinstate Monica Jan 31 '17 at 15:12
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Move the dang light and receptacle to a proper circuit

Since you indicated you had a 120V/20A circuit in the attic in addition to the 240V/60A circuit your AC installer stupidly bootlegged the light and receptacle off of, you can simply have the wiring for the light and receptacle combination moved over to the 120V/20A circuit -- just find the nearest junction box and tap the circuit there with the power off, minding your box fill of course! You'll want to turn the aux heater off at the breaker before removing the bootlegged circuit from the disconnect, too.

If you didn't have any 120V circuits in the attic, I would have recommended that you switch the light fixture out for a 240V fixture, but that runs afoul of 210.63 which requires a 120V receptacle there for the HVAC serviceperson to plug tools into, and a transformer just isn't cost effective here.

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  • Any issue with cutting a wire and adding a new junction box accessible from the attic? I don't think there is an existing one very close. – jmpreiks Feb 1 '17 at 3:16
  • @jmpreiks -- provided you can get enough slack in the line to have enough wire sticking into the box after making the cut, sure, go ahead. If not, you may need to use two junction boxes and an extra length of 12AWG NM... – ThreePhaseEel Feb 1 '17 at 4:41

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