10kw electric garage heater

motoguy128

Jamie Hall said:

To add a bit to @JUGHNE 's very careful and sensible underfusing of the circuits in the church -- something I applaud wildly over here! -- if working with an older structure, even a residence -- and here I'd say older being anything much before the mid 1960s -- never assume that just because the panel and some of the more visible wiring has been updated that all of it has. There may well be stretches of rubber and fabric 14 gauge wire -- or smaller -- hiding out there. Bottom line -- if you don't need 20 amps, say, and are not positive that the wiring is rated for that, end to end, what's the harm in going for 15 amps?

Words to live by.  First thing I did was swap all the 20a fuses in my upstairs sun panel with most all the original k &t that runs through the attic with 15a.  

Since then I’ve been slowing replacing circuits as I’ve done renovations.  I may eventually just run two new circuits with 15a arc fault beakers from the basement main panel to feed all that remains.  Down to about 45 led bulbs total and 6 ceiling fans.  So around 800w per circuit give or take if everything was on at once.  

mattmia2

If there is only lighting on the k&t, the load isn't going to change. A slightly smaller breaker isn't really going to add additional protection, the fault will be a short or more likely an open. An arc fault breaker will give you far more protection than a slight change in overcurrent protection.

Fixtures then and now are allowed to have smaller fixture wire, the load of the fixture is still far less than the rating of the wire.

JUGHNE

IMO, the largest risk with K&T is the integrity of the joints.
Originally they were to be wrapped, soldered and taped.
Many additions were made to the original by just wrapping and maybe taping. The none soldered joint will work loose and overheat, not necessarily arcing that AFCI would see.
Then all this is buried in 12" of insulation.
Dropping the OC protection sizing would force one to keep the load down and those bad joints cooler.

As for fixture wire, yes, it is rated for higher current ratings.
But if a bulb socket shorts outs, that fixture wire will be overloaded until the CB trips.
In the church case, the sockets and fixture wiring are that 50+ years old and the insulation a little frazzled.
Also there is about 10 feet of chain hanging the fixture.
Grounding to the J-box is only thru AC type cable of the same age. Grounding for the fixture is only thru the chain.
Ground

Jamie Hall

Nightmares of the past. When I was an apprentice sparky, I remember making countless joints -- straight splices, T splices, the lot -- carefully wrapping and soldering and taping, with every step inspected and criticised. Did you have to remind me, @JUGHNE ?

So much depended on workmanship. Grounding through the AC cable is actually pretty good -- provided the armor is securely fastened to the junction boxes. Grounding through K&T is, of course, non-existent. Further, K&T was never meant to be surrounded by insulation!

My own feeling -- which has nothing to do with the NEC -- is that for older AC and older light fixtures, like your hanging lights but also many many wall fixtures, arc fault breakers are the preferred protection (pity they're so darned expensive...). Will they work on circuits which do not have a ground? The literature is... not clear. Perhaps someone knows?

ChrisJ

Well.

While it's not the most derailed thread I'm thinking it's in the top 5.....

Canucker

ChrisJ said:

Well.

While it's not the most derailed thread I'm thinking it's in the top 5.....

Not completely derailed. At least we're still talking about electrical work

PC7060

Jamie Hall said:

....arc fault breakers are the preferred protection (pity they're so darned expensive...). Will they work on circuits which do not have a ground? The literature is... not clear. Perhaps someone knows?

Jamie - yes,  both AFCI and GFCI breaker function properly on 2 wire circuits with no safety ground. Price has come down quite a bit in recent years especially on the combo AFCI/GFCI units.

Re the workmanship, when I rewired my old house, I found the old K&T work to be impeccable. It was all the hack that had occurred in the intervening years that scared me. 

JUGHNE

Chris, wait until some food recipes show up before you judge!

ChrisJ

JUGHNE said:

Chris, wait until some food recipes show up before you judge!

I think that went over my head?

JUGHNE

Recipes would be further derailment, getting it into perhaps the top 2.

mattmia2

If the socket actually shorts it would trip the overcurrent protection before enough heat would be introduced in to the fixture wiring to cause a problem, which is why the exception exists in the first place. The bx can be an issue if there is a short and the metal is corroded so the current takes the long path, although gfci would protect you far better from that than any overcurrent protection. If an ungrounded fixture becomes live it isn't really a fire hazard(which is why at least at some point outlets above 7 ft weren't required to be grounded). Most 50+ year old fixture wore was type af which adds additional protection.

I would like to know more about how an afci works. I thought it looked for the waveform of an arc(or more likely a transform thereof) so it would detect faults between phases/phase to neutral/phase to ground and poor connections but I do not know.

Solid_Fuel_Man

AFCI breakers are a bit of a hoax if you ask me. There are many YouTube videos of electricians attempting to create an arc to trip them w/o success. 

AFCIs started (from my understanding) with the utilities using new fangled computers to detect a fault on their lines. As time went on and electronics became smaller someone decided it would be a great idea to make a circuit breaker sized arc detection device. 

Trouble is, the utility companies dont expect any natural arcs on this lines and can now pinpoint how far down the line one exists. In a home setting there are many appliances which naturally create arcing, vacuum cleaners, or anything with a universal (brushed motor running on AC) motors. Therefore there was a rash of nuisance tripping in the beginning. As well as the natural capacitance on having a hot and neutral at a perfectly spaced distance within a cable (romex). 

All of this us calculated and calibrated for at the utilities and their system isnt just a microchip in a circuit breaker. We get a microchip in a $50 breaker which has been numbed up enough to not nuisance trip. 

Houses burn from "glowing connections" not from arcing IMHO. Glowing connections are from those twisted connection on K&T after the solder has melted away....or an improperly twisted connection with a little steel spring (wire nut) holding it together. 

Sorry....I know this has nothing to do with a 10kw heater, but I'm very passionate about electrical safety as it's one of my jobs.