Overheating Sequencer wire

[Manitoba Bill]

My 15KW El. furnace has 3 sequencers.
http://mobilehomerepair.com/phpbb/album ... ser_id=108

http://mobilehomerepair.com/phpbb/album ... ser_id=108

I have replaced the 3 white, 240V wires but just around this time of year one of them starts to overheat and eventually break at the crimp joint nearest the seq.
I replaced all 3 with #10 dryer wire and had 1 fail last year and another is overheating this year. The furnace is old but had the original wiring until last year. All the other 240V wires are original.

I even put the original btm. wire back in when the first/new wire failed last year and it is still usable. (Not in this picture.)

I assume the problem appears now as the furnace is running longer but seems to last the rest of the heating season intact.

I could replace the wiring with heavier wire but wonder if another condition is causing the failure. A change of resistance in the circuit?

Thanks in advance.[/url]

[Robert]

Hi Bill,

You definately don't won't to go to higher wire than #10. That's high enough for the wiring.


With it continuing to overheat one of those over and over, the problem lies in over amperage from somewhere.


If it is incoming to sequencer from breaker, check/replace the breakers.


If it is outgoing from sequencer to elements, check/replace the elements.



Check for tight connections, good grounds, if ok, then one of those has become weak and pulling to many amps.


Is the furnace cycling on/off at correct time lapses or is it remaining on for extended periods, longer than normal ?


Get an ammeter and take amp readings and compare to furnace specs.


Take care and best wishes,
Robert

[Manitoba Bill]

Thanks for the info, I always assumed if the 3 elements were working they were o.k. Maybe the res. has changed and has led to my having to change seq. so many times with a greater draw through them.
I drew a red line in the second picture where the wire exits the seq. and enters the elements.

I had another HDD failure and will check the res. of the 3 elements
after I disc. the left lead. Power off at the mains, of course.

The furnace was cycling properly just longer with the temps around zero theses days.

Thanks, will get back with results over weekend.

[Manitoba Bill]

I checked the 5KW elements and all read 11.3 ohms on a digital meter.

I average one new seq. per heating season. Klixon 60000EO-106

[Robert]

Hi Bill,

That will tell you the elements are not broken and have good continuity.


Need an ammeter to take amperage readings with unit energized.


If wires are melting, then there is high amperage somewhere.


Elements are most common for this.



Thanks,
Robert

[Manitoba Bill]

Robert; sorry I didn't get back sooner. I wasn't able to borrow an amp meter and had a PC crash.

I replaced the broken new wire with the original wire.

I also noticed all the new wires broke right where they come out of the crimp connected to the seq.

I think that may be a clue to why they have failed but no solution.
Trying diff. crimps and maybe soldering also to see if they fail.

(Prob. in the coldest night.) LOL

[Robert]

Hi Bill,

Why sure, nothing fails when not needed,LOL. Be sure they are correct wire size(10awg/12awg) and be sure it is rated to at least 105*C thermoplastic.


Be sure crimp terminals are high heat rated.


You might find a decent Ammeter (wrap-around clamp jaw type) cheap enough on the net for home use.


That will actually tell you condition of the element coils.



Take care and best wishes,
Robert