Voltage Drop

Reply

  #1  
Old 03-22-15, 10:27 PM
Member
Thread Starter
Join Date: Mar 2013
Location: USA
Posts: 22
Voltage Drop

Hi. Bought a 30yr old house in MA.

Noticed when the microwave runs, the kitchen lights dim. I replaced all the lights with CFL/LEDs and now they don't dim..but still have a slight flicker.
Doing some digging I have found a substantial voltage drop at the Microwave outlet.

I'm hoping to find out if this is a problem (will damage anything), or any easy fixes.

Here are some details.

--15A circuit. Long run from electrical panel at far side of garage to opposite side of house where kitchen is.
--On same circuit as microwave are 10 recessed lights, dinning room light fixture and about 3 outlets in the dining room (WAY too many loads).
--Before running microwave (with or without lights on) I have 120.5V.
--Running microwave drops voltage to 106V at that receptacle.
--Microwave is pulling 15.5A and 1520W while running on this outlet.
--Another outlet on same circuit drops from 120V to 109V.
--Another nearby 15A outlet that is not on the same circuit drops to 117.5V.
--Nearby kitchen outlets that are 20A actually go up 1V from 120V to 121V while the microwave is running.
--House has only 100A service.
--Furnace, water heater, stove, dryer are all gas.

I guess first off is that Microwave should be on it's own dedicated 20A circuit.

Other than that, are all the voltage drops normal? Or is there another problem somewhere...

Thanks!
 
Sponsored Links
  #2  
Old 03-22-15, 10:42 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,587
The circuit for kitchen receptacles should not have lighting on it. It did not meet the code when built.

That voltage drop is excessive. It may indicate a loose connection and should be investigated before it cause issues.
 
  #3  
Old 03-22-15, 10:52 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 46,124
Microwave is pulling 15.5A and 1520W while running on this outlet
Actually... with that kind of load.... the voltage drop you are experiencing on #14wire is close to normal. Obviously the microwave requires its own 20A dedicated circuit.
 
  #4  
Old 03-22-15, 11:10 PM
Member
Thread Starter
Join Date: Mar 2013
Location: USA
Posts: 22
My guess is the wire is 100' or more in length since the wires run up into a knee wall, across the garage, house, then down into the kitchen.

I wonder if the house didn't have a microwave at one point and to add it, they just tied into the lighting circuit...
 
  #5  
Old 03-22-15, 11:16 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 46,124
That is very possible. With today's high powered appliances all kitchen receptacle circuits need to be 20A.
 
  #6  
Old 03-23-15, 12:24 AM
Handyone's Avatar
Forum Topic Moderator
Join Date: Aug 2000
Location: U.S.
Posts: 5,451
IF this is an over the range Microwave/Hood Combo:

This is a common problem. The house originally had a standard vent hood and it was typical to feed power to it from the lighting circuit, which was fine.

Homeowners change out these vent hoods to a Microwave and the lighting circuit simply can't handle the power demand.

Whether or not this is over the range, the solution is to run a dedicated 20 amp circuit for microwave use only.

It would still be prudent to check for any loose connections. But that is beside the point of providing a circuit for MW.
 
  #7  
Old 03-23-15, 10:26 PM
Member
Thread Starter
Join Date: Mar 2013
Location: USA
Posts: 22
Thanks everyone for the help.

@Handyone, I think that is it - it is an over-the-range microwave and was probably just a vent originally.

Just tonight I found an outlet behind the fridge (unused) which turns out is on its own 20A circuit. this is next to a small counter. So when the kitchen was built my guess is the microwave sat on the small counter and later on the home owner upgraded to an over-the-range microwave.

Now I just have to figure out how to move that dedicated 20A outlet from behind the fridge to the over-the-range...
 
  #8  
Old 03-23-15, 11:07 PM
Handyone's Avatar
Forum Topic Moderator
Join Date: Aug 2000
Location: U.S.
Posts: 5,451
Now I just have to figure out how to move that dedicated 20A outlet from behind the fridge to the over-the-range...
That's where we come in

If you have a basement or attic, that helps a lot. Especially if the cable comes from attic, it might reach the Microwave area or a junction box can be used.

Try to trace where cable originates, and we can go from there.
 
  #9  
Old 03-24-15, 09:46 PM
Member
Thread Starter
Join Date: Mar 2013
Location: USA
Posts: 22
Tracing it is the really tough part...

All the wires leave the box in the garage and go into the wall and up into a knee wall space on the 2nd floor. There are about 20 bundled wires together there with no IDs.

They travel along the knee wall above the garage to the other section of the house where 2nd floor wires go up into the attic and first floor wires go between 1st/2nd floors. The ceilings have strapping (1x2s) that run perpendicular to the joists. So the wires I have seen run just above the ceiling drywall in the spaces created by those strapping pieces.

I need to remove a couple recessed lights, hold my phone up in there and take some video to see if I can find the wire that goes towards that 20A outlet.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes