Electrical question

[MF294-4]

I hate to even ask an electrical question but here goes. Redoing some lights on a building I have. Neutral and ground tied together at the breaker panel. 90 foot run to two switches. One switch goes to 3 new t8 fixtures with six lamps with two electronic ballasts in each. The other switch goes to 2 mercury vapor, 2 cfls, and a 65w outdoor light. At the switch I have a small voltage between the neutral and ground. 2.5v with everything on. Less if the t8 are off and a lot less if you just turn the mv and cfls off. It is also less until the mv lights warm up. No voltage between the ground and neutral at the breaker panel. Looks like everything is wired ok. This voltage doesn't seem to be coming from any one fixture. Checked the continuity on all the runs.

 

[dr sportster]

Meters are not good for things like that if you get concerned about 2-3 volts. Use an Ideal tester and see if it lights up the low voltage light. Could be slight induction from the long run. { assuming you are coming from the main panel all is well]

 

[Bob]

Are you checking with a simple mechanical meter or an electronic unit that MAY be getting confused by electrical noise from the lamps and ballasts?

 

[MarkB_MI]

As I understand it, you are measuring voltage drop on the neutral conductor. With the two mercury vapor lights, you must have around 600 watts total load, which is 5 amps at 120 volts. Assuming you used 14 gauge wire, the drop from neutral to ground should be about a volt, so your drop is a little high. Recheck all your connections. If you're concerned about the drop, consider installing larger gauge wire from the panel to the switch.

 

[David G]

That is a pretty long run for 14 gauge.

 

[Greg K]

It could be induced voltage on the ground wire. Typically on a 3 way switch there is 20 volts on the traveller wire that is not being used, I think induced by being inside the switch with power. Like someone else said, make sure all connections are tight and make sure you have a ground rod too.

 

[Andy Martin]

I guess you should expect some voltage drop in order to move the amperage to and from the switches. So how does the hot wire measure, to ground, both at the panel and at the switches. If it's 120v at the panel and 117.5 at the switches it would seem you have the same voltage drop in the hot wire and neutral. Current flow does not come for free, it always costs voltage.

 

[John T]

With a load applied (lights on), the Grounded Conductor (Neutral) is carrying normal return current and subject to wire size and length, I would expect some, albeit small, voltage drop across the run. The Equipment GroundING Conductor if alls well and wired correct and no faults, should be carrying NO current (designed for fault current ONLY). When wires carrying current are in parallel close together there can be some, albeit small, induced voltage but it takes a good quality high impedance volt meter to accurately measure that.

If there are any minor high resistance low current shorts creating low current in equipment grounding conductor, such can cause voltage drops also, and such can be in light fixtures or ballast or wiring, hard to say whatand where.

Of course right at the panel where Neutral and Ground are bonded there shouldn't be any voltage drop across a basic short circuit, but the further away and the more devices and wiring and ballast and fixtures and possible minor high resistance shorts, its not hard to imagine a voltage potential between N and G. HOWEVER what it actually IS versus what a meter may say, depends on your meter type and quality.

Best I can say not being there and not knowing your meter.

John T

 

[buickanddeere]

There is VD on both load current carrying conductors.