I just installed a ceiling light in my kitchen, and now I measure a
47V (AC) difference between the light's ground wire and its neutral
wire. Is this normal, or could the ground wire be floating?
No, that is certainly not normal. Check the neutral and ground
connections in the panel, as well as anything that uses those horrible
spring loaded push-in terminals, those are notorious for developing bad
connections, IMO they ought to be banned.
If you are using a digital voltmeter, you could be seeing an open
circuit on the ground wire at the fixture. However, that being said, if
you have an open neutral at the breaker box or service entrance, you
have a serious condition warranting that you call for the utility
service or an electrician immediately. Fire and death by electrocution
are possibilities. Do any appliances or lights behave as the voltage is
too high or too low? If so, you have a serious problem.
If the fixture is working then leave it alone. If the fixture is not
working remove it and hook up a rubber pigtail socket and bulb to the
ceiling wiring to check it. Stop using your voltmeter. I'm guessing that
you are checking the voltage between the neutral with the fixture lit and
the grounding conductor.
I concur. Work your way back from the fixture with a voltmeter and see
where you lose that 47V.
Story about spring loaded terminals: I helped a friend diagnose a
flickering lights problem at his house. It seems that one circuit,
heavily loaded was fed through a receptacle using these spring loaded
contacts (in one set and out the other). It was the first device on the
branch circuit and was easy to diagnose. Although nothing was plugged
into it, the device was hot (thermally)!
I just had a circuit go dead in my house the other night, tracked it
down to the very same problem. I decided that while I'd already messed
up all the clocks finding the right breaker, I'd use that opportunity to
shut things down and replace the last few of the original upstairs
receptacles I hadn't gotten to yet and in that process I found one more
blackened corroded wire that had been arcing and was a failure or fire
waiting to happen.
The contact area is simply too small, it heats up and then the spring
loses tension and it starts to arc and heat up more. These things are a
safety nightmare, I will never understand why the NEC is so nitpicky
about some things yet lets major issues like these slide right by. Spend
a few bucks more for decent receptacles, it's cheap insurance and peace
of mind, not to mention plugs won't start falling out in a few years.
More than a few volts between the neutral and ground indicates that they are
not connected together. If they are properly connected together in the
entrance panel and the fixture is working, the ground is disconnected
somewhere (floating). Use a bulb in a pigtail socket to check this. It
should light from hot to neutral and from hot to ground. Be careful as a
floating ground can cause dangerous voltages to appear on supposedly
grounded metal parts, especially if you connect a load from hot to the
I'm not sure if these things are still available. All I've seen at the
local Home Despot are screw terminal types. Either the basic 'wrap the
wire around the screw' or the 'stick the straight wire in the hole and
apply pressure via an internal screw and clamp'. None depending on a
Besides that, I don't like using receptacles for a feed-thru. Pigtails
wherever possible, unless the box is too small to contain the extra
wires and nuts.
I think this is scary advice. The OP seems a bit out of his depth here.
He would be better advised to hire a competent electrician to get to the
bottom of this situation. There may be a perfectly rational explanation
for the voltage between N and G, but it also is an indication of a truly
When my son bought his house a few years ago, I found out that the
electrical system was upgraded by using grounding receptacles. Some were
found in the bathroom. The only problem was that no grounding conductor
was present. Everything would work as well as could be expected until
you become the grounding conductor. There probably are many such gotchas
Worst case is that the test light will illuminate connected from hot to
neutral. But it will be dim due to high voltage drop and the person
doing the test will not notice. A high resistance connection will get
HOT under load and may create a fire hazard. If a hot or neutral is wide
open, nothing works, but nothing gets hot.
*Granted. However the OP has failed to post any details. He didn't say if
the fixture was working correctly or not. He didn't say how he came to find
the voltage discrepancy. He didn't say why he changed the light fixture. I
just made some assumptions that everything was working fine and he was just
playing around with his volt meter. If the OP cares to furnish more details
then perhaps my response will be different
If its a DVM then yes you see that often. In fact, I would be more
worried if I saw 0 volts between neutral and ground when using a
DVM... because that meant that somehow my neutral got grounded and now
my ground is a load carrier (a situation you never want to see). Get
a low-impedance analog VOM meter and re-test it, you will see a much
lower or zero volts. Try a neon tester, it probably wont light. The
47V with a DVM is most likely induction current easily detected by the
DVM which has a very high impedance able to detect small current.
That is why I thought that OP was out of his league. Apparently he
thought so as well because he hired a presumably competent contractor. I
think that showed good sense on a situation that many people would feel
falsely competent to handle.
A few years ago, I hired a competent electrician to track down and
replace a poorly connected neutral conductor. I had diagnosed the
problem but had not pin-pointed where it was. That turned out to have
been a good decision because he was experienced in such matters and I
was not. I am confident that I could have located the problem but it
would take ten times as long and I would not know the best way to
Oops I missed the post that the OP found the open ground, but I have
seen all kinds of wierd readings on normal wiring if you use a DVM.
Also neutral problems scare me more than working on hot leads. Thats
because hot leads always simply terminate and their breakers are 1 to
1. So you would have to consiously put your body "in series" with the
current flow even if you are dumb enough to not trip the breaker.
Whereas neutrals travel all over the house, so if you open a wire cap
on a bundle of neutrals that you find in a box somewhere, even though
your breaker is tripped on the circuit you think is correct, that
bundle may still have some current flow from a different branch that
is live. So if you happen to separate and grab two of those neutrals
as you remove the wire cap, your body immediately is put in series
with a load carrying wire, not good. Being in series with a neutral
carrying 10 amps is instant death.
Neutrals actually require more safety caution than working with
specific hot leads especially when unbundling wire caps to insert
Exactly right. I might note that a high impedance voltmeter isn't a
good tool here.
That's what GFCIs are for. Place a GFCI upstream of these outlets
and all is well. Place stickers on the ungrounded outlets marking
them as ungrounded and you're even in compliance. Often, adding the
grounded conductor just isn't practical.