lights dim when garb. disp. turned on

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deckscrew

Member
We recently remodeled a duplex. A new 200 amp service with two meters was installed (100 amps to each unit). The downstairs unit is 1 bed, 1 bath and 1 small kitchen. The upper unit is 2 bed, 2 bath with updated kitchen. There is not an AC unit or hot tub in the larger unit, but there is a electric oven/micro unit requiring a 40 amp circuit.

When the garbage disposal in the upper unit is turned on the lights in both the upper unit and lower unit dim pretty noticeably. The appliance lights in the micro/oven unit and refrigerator also dim. When the lower unit disposal is turned on this does not happen. The upper unit unit disposer (3/4 hp, 11 amps) is on a 15 amp dedicated circuit per the manufacturer's recommendation.

The owners are worried about this situation and would like it repaired. They are worried there is loose wiring somewhere that could cause a fire. My electrician doubts it is loose wiring because the appliances lights, which are on their own circuits, and the lights in the downstairs unit which are on existing circuits and wiring are also dimming.

My electrician is out of town until next week. My electrician thinks this is a problem with the power company or loose wiring at the service entrance. The owners are insisting I hire an electrician to find the problem ASAP.

Is this a fire hazard, and should I hire an electrician, or should I wait for the electrician who did the installation to fix the problem? Has anyone else run into this kind of a situation

Thanks in advance.
 

dreamsville

Senior Member
Location
Michigan
Sounds like maybe a loose nuetral connection. Maybe in the main panel, meter can or possibly the service loop or utility supply. :smile:
 

COFFEE TIME

Member
Location
PHILA PA
We recently remodeled a duplex. A new 200 amp service with two meters was installed (100 amps to each unit). The downstairs unit is 1 bed, 1 bath and 1 small kitchen. The upper unit is 2 bed, 2 bath with updated kitchen. There is not an AC unit or hot tub in the larger unit, but there is a electric oven/micro unit requiring a 40 amp circuit.

When the garbage disposal in the upper unit is turned on the lights in both the upper unit and lower unit dim pretty noticeably. The appliance lights in the micro/oven unit and refrigerator also dim. When the lower unit disposal is turned on this does not happen. The upper unit unit disposer (3/4 hp, 11 amps) is on a 15 amp dedicated circuit per the manufacturer's recommendation.

The owners are worried about this situation and would like it repaired. They are worried there is loose wiring somewhere that could cause a fire. My electrician doubts it is loose wiring because the appliances lights, which are on their own circuits, and the lights in the downstairs unit which are on existing circuits and wiring are also dimming.

My electrician is out of town until next week. My electrician thinks this is a problem with the power company or loose wiring at the service entrance. The owners are insisting I hire an electrician to find the problem ASAP.

Is this a fire hazard, and should I hire an electrician, or should I wait for the electrician who did the installation to fix the problem? Has anyone else run into this kind of a situation

Thanks in advance.

i'm thinking maybe a bad motor or a bad connection...(locked rotor currents) 6-8 times npa. but your not having this problem when the lower unit is turn on.are both garbage disposal the same size? are you sure of the 11 amps? in the code book it shows 13.8 amps for a 3/4 motor.either way you will need an electrician to check it out.
 

480sparky

Senior Member
Location
Iowegia
No the lights are on separate circuits

OK, maybe next time I should read the OP a bit better.

I'd suspect something in the service as well. If it's dimming both units' lighting, then I'd start at the first point in the service the two are tied together and work towards the utility.

Contact the POCO and have them check their connections all the way back to the transformer.
 

benaround

Senior Member
Location
Arizona
If the G.D. is the only thing to make the lights dim, then I have a hard time thinking that

it is a problem at the service. I'm inclined to suspect the G.D. itself or the connections in

the motor or a bad connection, loose connection, bare connection, ungrounded short ( to

the metal sink and metal piping) with lost EGC.
 

active1

Senior Member
Location
Las Vegas
I would check the voltages at the panels when turning on the disposal. If you see one leg voltage drop and the other raise higher it would be a neutral issue.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
081205-1917 EST

deckscrew:

If there is 120-0-120 service in both halfs of the duplex, and we assume both disposals draw the same inrush current and both are 120 V units, then it is not a neutral problem.

In the duplex half that has the disposal that causes dimming look for some circuit that is on the opposite phase from the disposal. One way to troubleshoot this is to look in the breaker box. Identify the breaker that supplies the disposal. The breakers on the opposite side of the panel should be on the other phase. Look at the labeling of these and see if this points you to an outlet that you can plug a light into or some place where there is already a light. The point here is to see if comparable dimming is occurring on this opposite phase. If not, then there is a high resistance in the hot line preceeding the two service meters that is supplying the phase to which that disposal is connected. And it means the other disposal that does not cause dimming is on the opposite phase.

If lights dim on one phase and brighten on the other phase, then you have a neutral problem.

.
 

mxslick

Senior Member
Location
SE Idaho
I don't think it's a loose neutral, but I'd bet on a bad connection or main breaker (is it Murray, Crouse-Hinds or shudder Zinsco) on ONE LEG.

I'd also bet that the disp and all the affected lighting is on the SAME LEG.

So check all the hot legs, meter, POCO connections, and main and/or subpanel breakers.
 

benaround

Senior Member
Location
Arizona
deckscrew,

Here's something you can try yourself, do you have a vacuum cleaner at the duplex ? Plug

it in here and there throughout the two units and see if the lights dim like they do when the

disposer is run. If they do then the problem is likely as others have mentioned, if not then

it is the disposer.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I would not be looking for a bad neutral or a loose connection....it sounds like a defective disposal that it pulling way too much current on start up. A loose connection on the disposal circuit would act like a reduce voltage starter and would limit the inrush, not make it greater. A neutral problem should, as others have said, make the lights get brighter on some of the circuits and dimmer one the others.
 

deckscrew

Member
Thanks for all the replies. I got a number to call Insinkerator. The unit is a 3/4 HP with 8.1 amps listed on the plate on the side of the unit. I checked all the wiring and all connection were good. The literature did not even call for a separate circuit, but we provided a dedicated 15 amp circuit for the GD.

I have a saw that draws that rated at 9 amps. I'm going to plug it into the outlet and see what happens.
 

JES2727

Senior Member
Location
NJ
081205-1917 EST

Identify the breaker that supplies the disposal. The breakers on the opposite side of the panel should be on the other phase.
.

Not on any panel I've ever seen. The phases alternate from top to bottom - a,b,a,b,a,b,a,b, and so on.
 

COFFEE TIME

Member
Location
PHILA PA
Thanks for all the replies. I got a number to call Insinkerator. The unit is a 3/4 HP with 8.1 amps listed on the plate on the side of the unit. I checked all the wiring and all connection were good. The literature did not even call for a separate circuit, but we provided a dedicated 15 amp circuit for the GD.

I have a saw that draws that rated at 9 amps. I'm going to plug it into the outlet and see what happens.

i still think it's the garbage disposal. but if it's still happens when you plug the saw in you may want to look at the single pole switch controlling that outlet or the breaker...
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
081206-1858 ESt

You are correct and I should have said something like the phase changes alternately from one adjacent breaker to the next.

Certainly two pole breakers would not accomplish their function if the alternation did not exist.

.
 

480sparky

Senior Member
Location
Iowegia
081206-1858 ESt

You are correct and I should have said something like the phase changes alternately from one adjacent breaker to the next.

Certainly two pole breakers would not accomplish their function if the alternation did not exist.

.


Until you get into a Pushmatic panel. ;)
 
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