I'm Stumped

[Bib Overalls]

Helped a friend with the wiring in his shop today. It is an old building slightly larger than a one car garage with it's own metered 100 amp 120V service.

Some of the wiring is in the walls and some has been strung around on the outside. It is a real mess and we are working to sort it all out.

Today I put up three 4' fluorescent light fixtures and wired them back to the panel. The circuit is on it's own breaker.

I also wired in two outlets on dedicated breakers, one on each leg.

Here is the funny part. When the lights are on they are about medium intensity. If I plug the shop vac into one outlet and turn it on the lights draw down even more. If I plug the shop vac into the other outlet and turn it on the lights get brighter.

I suspect a weak leg but I don't know how to check for that. Both legs have 120 V but that does not measure load potential.

Has anyone ever experienced anyrhing like this? Any ideas as to what is causing this?

Told my friend we need to abandon the wiring in the wall and rewire all of the outlets and lights on the surface. This won't fix a weak leg but it will be much safer than what he has now.

 

[Stuff]

It means your neutral is loose somewhere between the panel and the street transformer. You should be calling your power company to check it out.

 

[AlwaysFixingSomething]

Loose or damaged main neutral or circuit neutral.

Measure the voltage at the main panel on each leg and tell us what you get.

 

[zmaxmotorsports]

Check all connections inside of panel to make theyre tight ,including feeders.
A lose or open neutral will normally show a voltage between 60-70 volts.
Post a picture of inside of panel if you can.

 

[Milton Shaw]

Put a load on one leg from the panel and then measure the voltage of each leg to neutral. You have a loose neutral but they show up better with a load on one leg. Power company problem as you say it has it's own meter.

 

[BillK]

Bib,
I have had a couple of bad breakers cause similar problems here at the shop. If there is a main breaker it could be doing it also. Start at the input side of the main breaker and go from there. Plug in a heater or I guess your shop vac, anything that will put a decent load on the system. Work your way forward from the main breaker until you find where the voltage is dropping.

 

[justsam]

Helped a friend with the wiring in his shop today. It is an old building slightly larger than a one car garage with it's own metered 100 amp 120V service.

I also wired in two outlets on dedicated breakers, one on each leg.

I suspect a weak leg but I don't know how to check for that. Both legs have 120 V but that does not measure load potential.
QUOTE]


I am a little confused with the above statements. Is there 120 or 240 coming into the single car garage?

How is the garage panel fed? Two hots, a neutral, and local ground?

I agree it does sound like a bad neutral connection but need clarity on 120/240.

 

[Bib Overalls]

Shop has 120/240 service. two hots and a neutral. Going up next Saturday to wire up a couple of additional outlets and do some additional testing. The panel is a mess. I'll report what I find.