Posts: 13,412
Threads: 0
Joined: Jun 2004
Location: Texas
I was up on the metal roof of my carport trimming trees with the electric chain saw and had a thought.
What if the extension cord I was dragging along cut into the edge of the metal roof and shorted, causing the whole roof to become "hot"? If the roof were grounded, it may not become a hazard. Would the ground fault breaker trip?
Shouldn't all metal roofs be grounded anyway since they can be exposed to wiring not on a ground fault circuit? How would this be done? In some cases you couldn't be sure there isn't a bad connection from roof panel to panel (corrosion), in which case, you would have to loop a ground to each roof panel.
Probably too much thinking?
Posts: 1,998
Threads: 1
Joined: Aug 2016
(01-12-2017, 01:03 PM)daddo Wrote: I was up on the metal roof of my carport trimming trees with the electric chain saw and had a thought.
What if the extension cord I was dragging along cut into the edge of the metal roof and shorted, causing the whole roof to become "hot"? If the roof were grounded, it may not become a hazard. Would the ground fault breaker trip?
Shouldn't all metal roofs be grounded anyway since they can be exposed to wiring not on a ground fault circuit? How would this be done? In some cases you couldn't be sure there isn't a bad connection from roof panel to panel (corrosion), in which case, you would have to loop a ground to each roof panel.
Probably too much thinking?
If the roof was not grounded in any way, I would not count on the GFCI tripping as the only current would be very minor charging current from a capacitor effect. The GFCI should trip if you become the ground connection.
Grounding the roof is a good idea but the problems you mentioned are real. Take that same line of thinking and consider metal siding, gutters and downspouts. To be considered grounded every joint needs a bonding jumper or other mechanical means to assure continuity. Many gutters and down spouts have been energized from Christmas lights. Roly
[font="Helvetica Neue",Helvetica,sans-serif]Save[/font]
Posts: 4,904
Threads: 0
Joined: May 2010
I don't think anything would happen just like a bird on a power line
Posts: 13,412
Threads: 0
Joined: Jun 2004
Location: Texas
(01-12-2017, 04:53 PM)fixtureman Wrote: I don't think anything would happen just like a bird on a power line
If there weren't a GFCI and someone walked by and grabbed the metal roof for any reason, it could wake you up- heat up the coffee in the cup your holding and curl your straight hair.
Posts: 27,931
Threads: 0
Joined: Jul 2002
Location: Pacific ocean now much further away!
Lot of metal roofs here and none are grounded, make for a huge target for lightning.
VH07V
Posts: 1,531
Threads: 0
Joined: Jan 2007
The key words being grounded. You are not grounded on the roof. If the chord was cut and the power went to ground of the chord it will short out. Just like if you are in an accident and wires from the pole fall on your car, do not get out. You are not grounded but as soon as your foot hits ground you then complete a circuit. The tires of the car insulate you from the potential.
John T.
Posts: 1,407
Threads: 2
Joined: Jun 2003
No the roof won't become hot. That's a dead short and the breaker would trip immediately.
After reading your other electrical post if that's the extent of your knowledge, I definitely think you need to hire an electrician!!
Posts: 1,998
Threads: 1
Joined: Aug 2016
(01-17-2017, 12:45 PM)rwe2156 Wrote: No the roof won't become hot. That's a dead short and the breaker would trip immediately.
After reading your other electrical post if that's the extent of your knowledge, I definitely think you need to hire an electrician!!
What if just the hot leg was cut into and the roof was not grounded ? It would be hot then. Roly
Posts: 1,407
Threads: 2
Joined: Jun 2003
01-18-2017, 10:57 AM
(This post was last modified: 01-18-2017, 11:01 AM by rwe2156.)
No it wouldn't. Electricity always seeks ground so if the metal roof is not grounded, there is no potential difference so there is no current.
Same principle behind a bird sitting on a wire or the squirrel - until he reaches out and touches ground then he gets fried.
Posts: 1,998
Threads: 1
Joined: Aug 2016
01-18-2017, 11:11 AM
(This post was last modified: 01-18-2017, 11:13 AM by Roly.)
Think about it. There is no current but it is hot. When you plug in a extension cord and nothing is connected on the other end, it is hot just waiting for a complete circuit. Hopefully a person is not part of the circuit completing it. Roly
