ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
"Esoteric" countries and their wiring practices?
by Texas_Ranger. 04/20/19 07:00 PM
Norwegian power?
by Texas_Ranger. 04/20/19 06:27 PM
Welded Copper Connections
by gfretwell. 04/19/19 04:46 PM
Israel
by annemarie1. 04/18/19 02:35 PM
Water heater calculationsSo when I count calculati
by watersparkfalls. 04/13/19 12:43 PM
New in the Gallery:
What is this for?
Plug terminals
Who's Online Now
1 registered members (Scott35), 8 guests, and 8 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Interesting Knob & Tube setup #220012
03/29/19 09:38 PM
03/29/19 09:38 PM
B
BigB  Offline OP
Member
Joined: Mar 2004
Posts: 742
Tucson, AZ USA
We have replaced a lot of K&T over the years and seen a lot but this one takes the cake. The initial call was from smoke coming out of the closet ceiling. While we did not find a smoking gun wink when we first arrived (it was the next day after the reported smoke) we did notice the 14 gauge K&T was divided into three circuits all on the same 14 gauge neutral and all from the same 120 volt fuse box. So all three circuits were on the same leg of the service (*actually 4 if you count the door bell transformer). Of course all four fuses were the usual 30 amp ones rolleyes that we normally see. My theory is that the neutral got mighty hot and that is what was making the smoke. Two days of rewiring and we haven't found anything visibly burnt in the attic.

Work Gear for Electricians and the Trades
Re: Interesting Knob & Tube setup [Re: BigB] #220013
03/30/19 11:51 AM
03/30/19 11:51 AM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,348
Estero,Fl,usa
K&T is basically air cooled so it will handle more current than any cable or raceway wiring method although you still use the same ampacity charts. I imagine the smoke was just the dust burning off the conductors, similar to the first time you turn on the toaster wire heat strips in an air handler after a long time. Here in SW Florida it might be years since the last time you had the heat on.
Were any of the conductors discolored?


Greg Fretwell
Re: Interesting Knob & Tube setup [Re: BigB] #220015
04/03/19 12:49 PM
04/03/19 12:49 PM
T
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,448
Vienna, Austria
That's somewhat common in bodged wiring upgrades in central Europe. Cookers (ranges) usually have the elements connected L-N but take three phases to spread the load, either on a 3-pole 16 amp or three single poles. Two hob elements per phase and the oven on the third (it's rare to see anything with more than four elements and a single oven here, the typical load is 6.5-8 kW). However, if the incoming mains is only single-phase 2w but the installer sets up the cooker circuit for three-phase 4w, the neutral could see up to 3x16 amps. In Austria that's somewhat de-fused by the typical 25 amp limit on the incomer but in Germany the incomer could be fused at up to 63 amps.

I've seen that once or twice in Austria but decided to leave it - 2.5 mm2 and a 25 amp bottle fuse is marginal because of the slower overload trip of the fuse compared to a B/C MCB but unlikely to burn the house down and it was decidedly temporary - the installer had put back the original single-phase meter, jumpering all the load-side lives until the grid operator's subcontractor installed the new three-phase meter. Usually that shouldn't take more than a few days but in this instance it was about two months.


Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
HCE727
HCE727
Delaware County, PA, USA
Posts: 186
Joined: November 2005
Show All Member Profiles 
Top Posters(30 Days)
Popular Topics(Views)
254,533 Are you busy
190,770 Re: Forum
180,493 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.029s Queries: 15 (0.010s) Memory: 0.9528 MB (Peak: 1.0775 MB) Zlib enabled. Server Time: 2019-04-22 20:32:23 UTC