120 volt trouble shooting

[jacwjames]

This is a FWIW post, not RV related but useful

A friend called me yesterday, he has a large Hot Tub with all the bells and whistles.  About 3 weeks ago the control panel quite working, no display, so no functions.  The tub has a circulating feature with filter and chemicals.  The water got nasty pretty fast.  He called the Hot Tub company that installed it, two weeks to schedule and appointment, and they came out yesterday.  Checked the voltage at the subpanel and said the voltage was bad, charged him $240 and left (said they weren't allowed to work on anything past the subpanel).

He called me, told him I'd be there in ~ a couple hours.

Got there and checked voltage at the 60 amp double pole breaker, measured 124 on L1 & L2.   Checked the voltage in the subpanel voltage was 124 on L1 and 36 on L2 !!!  I did loosen and then retighten the lugs on each wire at the main breaker and then tested again, no change, still had low voltage on one leg at subpanel.

We did a visual check of the cable running from the main panel to the subpanel, had to go into his crawl space for this, NASTY stuff and wasn't really dressed for that but you have to do what you have to do.  We didn't find any evidence of a problem.

Back to the main panel, checked voltages again with the same results.  So I decided to take the wires loose and pull the breaker.  No signs of problems on the panel.  Flipped the breaker off and on, couldn't see any problems there.  But when I put the breaker back I switched wire location on each lug, made sure they were tight, I did this with the breaker out of the panel so I could more easily switch the wires.  Put the breaker back in and made sure it was seated good.   Harder to get the breaker in but I made sure wires were tight.  Check voltage, 124 on L1 & L2 at main panel.  Checked voltage at subpanel and had 124 on both L1 & L2, problem solved.

So my guess is that there was some corrosion on the one leg causing a voltage drop.  Testing using the lugs didn't test the wire connection.  So pulling the wires and reattaching them did the trick.  So just a FWIW post, this type of problem can easily happen in a motorhome, especially with the vibration from running down the road. 

No need to respond

[Tom Cherry]

4 hours ago, jacwjames said:

This is a FWIW post, not RV related but useful

A friend called me yesterday, he has a large Hot Tub with all the bells and whistles.  About 3 weeks ago the control panel quite working, no display, so no functions.  The tub has a circulating feature with filter and chemicals.  The water got nasty pretty fast.  He called the Hot Tub company that installed it, two weeks to schedule and appointment, and they came out yesterday.  Checked the voltage at the subpanel and said the voltage was bad, charged him $240 and left (said they weren't allowed to work on anything past the subpanel).

He called me, told him I'd be there in ~ a couple hours.

Got there and checked voltage at the 60 amp double pole breaker, measured 124 on L1 & L2.   Checked the voltage in the subpanel voltage was 124 on L1 and 36 on L2 !!!  I did loosen and then retighten the lugs on each wire at the main breaker and then tested again, no change, still had low voltage on one leg at subpanel.

We did a visual check of the cable running from the main panel to the subpanel, had to go into his crawl space for this, NASTY stuff and wasn't really dressed for that but you have to do what you have to do.  We didn't find any evidence of a problem.

Back to the main panel, checked voltages again with the same results.  So I decided to take the wires loose and pull the breaker.  No signs of problems on the panel.  Flipped the breaker off and on, couldn't see any problems there.  But when I put the breaker back I switched wire location on each lug, made sure they were tight, I did this with the breaker out of the panel so I could more easily switch the wires.  Put the breaker back in and made sure it was seated good.   Harder to get the breaker in but I made sure wires were tight.  Check voltage, 124 on L1 & L2 at main panel.  Checked voltage at subpanel and had 124 on both L1 & L2, problem solved.

So my guess is that there was some corrosion on the one leg causing a voltage drop.  Testing using the lugs didn't test the wire connection.  So pulling the wires and reattaching them did the trick.  So just a FWIW post, this type of problem can easily happen in a motorhome, especially with the vibration from running down the road. 

No need to respond

A wise electrical contractor helped me salvage a panel with a bit of moisture damage.  Not quite the same, but is along the same lines.  If a breaker is good and the panel is good, the common “field” trick is a toothpick and No A Lox.  Lowes sells a Gardner Bender product as well.  It is designed for preventing corrosion on mobile homes or installations with aluminum wire.  Think of a very abrasive toothpaste with ground up metallic fines.  You put a light (toothpick or small flat blade screwdriver ) coating on the panel lug(s) and the spring snap in contacts on the breaker.  BINGO.  That sort of polishes or burnishes (you use a suitable tool and remove obvious corrosion) when you snap in the breaker.  That was 20 odd years ago,  those 5 breakers, that got a bath, still work today.

Just passing on a trick that many journeymen electricians use…