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Electrical Question:

Question asked by Steve Schroeder.

I just inspected an older home with signs of knob + tube (although no K+T wire was actually seen). The BX cable from the furnace (2003) to the panel (relatively new 100A) did not have a ground wire. Under what circumstances can the casing serve as grounding?

Answer:

Armoured cable before they had bond wire had an aluminum strip that was bent over and secured under the connector. This was an acceptable means of bonding at the time of the original installation and the code is not retroactive. It’s difficult to determine when the cable was originally installed.

Regards ,

Trevor Tremblay

Technical Advisor, Northern Region

Electrical Safety Authority