I installed 6 flourescent light fixtures in my shop ( each fixture is 8 feet long with 2 high output bulbs) on a 15 amp circuit with 14 gauge wire. The flourescent fixtures have magnetic ballasts. I have 3 switches controlling the lights (two 3 way and one 4 way). The wires are warm to the touch. I measured a current of 12.8 amps when the lights are on. I will probably re-wire using 12 gauge wire on a 20 amp circuit (I may break up the lights an put them on two separate circuits).
Is 12.8 amps on a 15 amp circuit too much? I am surpised that the wires are warm to the touch and an electrician I know said that they should not be warm. Any thoughts? Thanks.
Replies
12.5 is not too much for a 15A circuit. Would be if pushing it if in was a single load but with multiple loads your fine. Warm is a subjective term. Rule of thumb is that if you can comfortable keep you hand on it, assuming your not a welder or foundryman with tollerence befitting the damned, your OK.
No need to upgrade or split the circuit as long as there isn't a whole lot more going on it. You can run it safely as a full 15A. A bit more for limited times. The breaker will let you know. That's why it's there.
The following two issues may or may not be related to the heat sensation the poster is reporting:
- I noticed on the sheath markings that some (NMD) wiring is rated for 60C degrees (this was US wiring) while Canadian wiring is rated 90C. The actual wire cross-section of 60C 14/2 is smaller than that for 90C 14/2. I'd have thought that each wire gauge was an exact specific diameter, but apparently there are variations. Canadian electrical inspectors will fail circuits wired with 60C US cable.
- Apparently cables rated for burial (NMW) aren't supposed to be used inside walls... as their insulative properties are designed for the heat losses of an underground environment. Could you confirm this?
Thanks 4LORN1.
The old 60C NM hasn't been made for a couple of decades. Late runs of this had the jacket colored baby blue to make it easier to spot. This stuff was used just like modern NMB. Wasn't much of an issue at the time as it was the best they had. Also most light fixtures were Bakelite or porcelain and anything stronger than a 60w bulb was rare. Sheet metal fixtures that conduct heat readily, hotter bulbs at 75w and up made 60C much more dangerous.Back in the 50s, before plastics technology improved, 60C was pretty standard for house wiring. It wasn't too many years since the 30s and 40s when most wiring had vulcanized rubber insulation with a cotton jacket that required the copper conductor to be tinned, coated with a lead/tin alloy, to protect it from the sulfur used to harden the rubber. Sometimes people will discover wiring they take for the more dangerous aluminum branch circuit wiring. A mistake easy to make because the tinning looks a lot like old aluminum. Way to tell the difference is to scrape the conductor or look at the end where it is cut. Both cases the copper shows through.If you have 60C wiring don't freak out. Selecting fixtures that are rated for it, ones that aren't are marked as such, is a good idea. Splicing on 90C wire pigtails and stuffing the connection in the bottom of the box, away from the fixture, is an option.Rewiring would be the ideal solution. Expensive but still cheaper than a fire. Some insurance companies, I hear and if a contractor does the job, might give you a discount.
I'm pretty sure that the 60 degree wire and the 90 degree wire are the same diameter. What's changed is the temperature tolerance of the insulation, and all new wire in the US is 90 (or better).The switch from 60 to 90 was made mostly because folks tend to over-lamp ceiling fixtures, and the 60-degree wire just couldn't hack a 60-watt fixture with 100-watt bulbs in it. You open up a ceiling fixture that's been in this situation (which is about 3/4s of the fixtures in existence) and you'll discover the 60-degree insulation is crumbling into dust.But back to the original topic, a wire carrying close to its legal load will feel fairly warm (not quite hot) to the touch. This is normal.
Typically you don't want to load a circuit any more than 80% of the circuit breaker rating. 80% of 15 amps is 12 amps, so you're just a little over that but I'm still a little surprised the wires are getting warm. I'd suggest going to two separate circuits, but upsizing to 12 gauge wire and a 20 amp circuit will also work.
Hey stuart, How have ya been?Saw your post and thought I would say Hello-----things were pretty quiet around here for a while but the bids are starting to come in so a steady flow should be just around the corner. I hope.....How about for you?Drop me a line sometime. Mike
I did not see anyone else mention it but I think I would check all my connections just for grins.
You may come out ahead upgrading some of the fixtures to the solid-state balast. I think you may get a drop in the amps.
If your lights are expected to be on for three hours at a time they would be considered continuous loads,and so shouldn't go over 12 amps on a 15 amp breaker.Yeah,I'd believe they're heating up your #14's.The solutions you point out in your post are the correct ones.
Anychance that a wire could be damaged? I believe that would cause them to heat up some. Similar to a bad connection...
Could be.
Pushing the legal limit on a branch circuit just isn't a good idea though.I had a repair job last month in grocery store that had a whole pipe full of wires that individually would have been legal, but collectively heated up the pipe enough to cause a meltdown.These were 20 amp circuits with 15 and 16 amps on them.The original installer didn't derate the circuit ampacities properly for the amount of conduit fill.
"Anychance that a wire could be damaged? I believe that would cause them to heat up some. Similar to a bad connection.."Not really.Unless it was a manfacturing defect the where the wire was made under sized any damage would be localized to a small area and the heat to that area.