DIY Home Improvement Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
650 Posts
Discussion Starter #1
In testing a suspect light socket for proper polarity, I plugged in a grounded extension cord to an outlet with a known good ground, and connected a multimeter between the shell of the socket and the cord ground. It read 123V, confirming reverse polarity.

I knew that this test shouldn't trip the breaker, but my interest is in why. If I connected the hot directly to the ground without a multimeter in between I would certainly hope it would trip. This is a 15A regular, non-GFCI breaker. Since the ground and neutral from that circuit are bonded at the panel, I guess it shouldn't matter whether I connected the hot to the ground or the neutral. Given that, is the multimeter simply acting as a normal load, just as a light would? Is the multimeter acting as a resister, keeping the amperage low enough not to exceed the limit of the breaker? How many amps does a multimeter typically draw in VAC mode? Thanks for helping me understand.
 

·
Registered
Joined
·
5,467 Posts
With any electrical path to ground,
weather the fuse/breaker blows depends on the amount of current flowing
with a digital multimeter it would be a very very small amount of current
No where near what is needed to blow the circuit.
A typical meter is 1M ohm per volt.
So at 120v, that is 120 meg ohms
120/120000000 = .0000001A
Thats micro-amps.
 

·
Registered
Joined
·
924 Posts
,,on your suspected reverse polarity, it could be the 2 fixture wires are reversed. Also, you may be getting a feed-back reading through other loads on the circuit instead of actual power there on the supposed neutral
 

·
Registered
Joined
·
650 Posts
Discussion Starter #7
,,on your suspected reverse polarity, it could be the 2 fixture wires are reversed. Also, you may be getting a feed-back reading through other loads on the circuit instead of actual power there on the supposed neutral
Thanks. It's a ceiling light fixture with three sockets fed from one cable. Two of the sockets had correct polarity, one didn't. The problem was reversed wires on that one socket. I reversed them and that fixed the problem.
 

·
Registered
Joined
·
650 Posts
Discussion Starter #8
Thanks to all for the explanations and info. I have a better understanding now.
 

·
Registered
Joined
·
997 Posts
the polarity on a light socket is only for security if someone accidentally touch the shell while switch is on. the shell is not grounded.
 

·
Super Moderator
Joined
·
20,923 Posts
It is for safety not security. A reverse wired light socket is a shock hazard if someone touches the shell when unscrewing the bulb with power on.
 
1 - 10 of 10 Posts
Top