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Thomas Stephenson

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I find myself in a situation which I cannot satisfactorily explain:

I added a 240 volt HVAC circuit to a fuse box piggybacked temporarily on the range circuit (the service change was scheduled for the following week).

One of the 2 the two main fuses (the fuse to the whole fusebox) blew a few days later. So 120 volt to ground from one leg and 0 to ground at the other leg. The customer reported a fire at the range and the dryer stopped working. The range outlet and the dryer outlet are both 3 wire (no neutral).

My question is is it possible for a blown fuse (dropped leg) to cause a fire in a range, and can that cause a dryer's permanent failure?

I expect that I know the answer, but you may imagine that the customer has lost faith in me and does not trust my answer.
 
Thomas Stephenson said:
I find myself in a situation which I cannot satisfactorily explain:

I added a 240 volt HVAC circuit to a fuse box piggybacked temporarily on the range circuit (the service change was scheduled for the following week).

One of the 2 the two main fuses (the fuse to the whole fusebox) blew a few days later. So 120 volt to ground from one leg and 0 to ground at the other leg. The customer reported a fire at the range and the dryer stopped working. The range outlet and the dryer outlet are both 3 wire (no neutral).

My question is is it possible for a blown fuse (dropped leg) to cause a fire in a range, and can that cause a dryer's permanent failure?

I expect that I know the answer, but you may imagine that the customer has lost faith in me and does not trust my answer.
Click to expand...

All the domestic range and dryers I have seen have a neutral connection.
Old fuse installations have a problem of allowing current to flow through 240 v heating elements such as dryers, ranges, and water heaters to the load side of the blown fuse and thru any hot to neutral connected loads. Usually the lights are dim when one of the heating loads are calling but I imagine it could possible cause problems esp with 120v electronic loads. This would/could have happened regardless of where you put the new A/C load. To the home owner you are guilty. Good luck.
 
I have found there is a law, similar to Murphy's, that states anytime an electrician walks into a residence with tools he is responsible for any related electrical failures for the next 6 months minimum :)
 
Draw it out

Draw it out

Depending on what the voltage drop is across the element I could see things on other circuit going bad but not the dryer.

Lets say it is an older range with manual switchs.

Voltage comes in on phase A goes thru switch, then thru element and out phase B.
Since it can't get back to phase B because of blown fuse.
Then it will look for anouther way back.
Lets say there is a light turned on with a switch that is connected to phase B.
Since the element is still looking for a way to make current flow it will flow thru the fuse feeding the light, then thru the switch and thru the light back to the neutral.

When this happens you get 120 volts divided between the two loads that are now in series giving LOW voltage to both. Some things like electronics don't like low voltage, and may go bad but not the dryer or range because you said no neutral.

Note: this happens allot when you lose a phase in three phase machines, coils for contactors melt when they can't pull in all the way and burn up.
 
Let's back up a minute. Chicken and egg here.
1. What came first, the fuse blowing or the range fire?
2. You tapped off the range fuse to feed the HVAC, but did not disturb the dryer circuit?
3. The main fuse (one of the two) blew, not the range or dryer fuse?
4. What are the values of these fuses?
5. Have you determined what caused the fuse to blow?

Frank DuVal
 
the 2 damaged devices are 2W 240 with EGC, correct?
how could current flow if 1 leg was open?
ground fault on the load side?

it sounds like the equipment blew the fuse, not the other way around, not single leg damaging the equipment
perhaps low voltage (high V drop) caused the damage to the equipment?
drawing excess current and blowing the main

the dryer is resistance heating, so low V would only reduce current/power, should not hurt it
might damage the motor if 240

stove
same, resistance heating (assumed, could be induction, but I doubt it in a home that still has a fuse box)

HVAC circuit
what was the equipment? heat pump? electric heat?
???

unfortunately the layman looks at it this way:
everything working
you make changes
and then trouble arises
you own it until you prove otherwise which may be impossible...especially with questionable practice, ie, 2 loads, HVAC/stove off 1 fuse set
 
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The range outlet and the dryer outlet are both 3 wire (no neutral).
Click to expand...

Might want to verify there is no neutral loads, I have seen ranges that don't utilize a neutral but have yet to see a dryer that doesn't have a 120 volt motor and 120 volt timer controls. If a range has an oven light it will normally be 120 volt, and it cost less to build the range to just use a neutral conductor then to transform that voltage within the appliance. Timer/clock on ranges is very likely 120 volts as well.

What happens when a service or feeder ungrounded conductor opens (including blown fuse) was described a few posts back, two (or more) items get put in series with 120 volts as the source. Range elements will just have a pretty extremely reduced output from normal but it won't hurt them. That leaves you with timer/controller as the item that possibly won't play well with the wrong voltage. Same for the dryer.

Same thing can happen if one ungrounded conductor becomes open for any reason not just a blown fuse.
 
Thomas Stephenson said:
I added a 240 volt HVAC circuit to a fuse box piggybacked temporarily on the range circuit (the service change was scheduled for the following week).

My question is is it possible for a blown fuse (dropped leg) to cause a fire in a range, and can that cause a dryer's permanent failure?
Click to expand...


This doesn't help now but may be good advice for the future. We have all done it at one time or the other but it's not really a good idea to temp things up and leave them unattended in a house that's occupied. You leave yourself open to any sort of blame for any thing that happens.

I can't see the need for AC at this time of the year so you probably temped things for the AC install. They could come back and check out the AC condensor after the new service is installed.
 
growler said:
This doesn't help now but may be good advice for the future. We have all done it at one time or the other but it's not really a good idea to temp things up and leave them unattended in a house that's occupied. You leave yourself open to any sort of blame for any thing that happens.

I can't see the need for AC at this time of the year so you probably temped things for the AC install. They could come back and check out the AC condensor after the new service is installed.
Click to expand...
He could have "temped" it in a more proper manner - and still would have had the same result when main fuse blows.

Does it make him look bad to the customer, yes.

If he hasn't given them a complete cost for upgrading the service yet -throw in the cost to repair the damaged appliances, tell customer they will be fixed and move on. If you must eat cost of fixing those appliances still may be better then getting bad word put out about your business, might even get you some good words for fixing them.
 
kwired said:
He could have "temped" it in a more proper manner - and still would have had the same result when main fuse blows.
Click to expand...

It may not have been the temped AC that even caused the problem but it will be hard to prove.

If either the dryer or the range shorted and blew the fuse it would also cause the same problem.
 
growler said:
It may not have been the temped AC that even caused the problem but it will be hard to prove.

If either the dryer or the range shorted and blew the fuse it would also cause the same problem.
Click to expand...
I agree, also have a suspicion increased load on the main fuse pushed it over and is the cause of blowing one of them. Unless it is easy to prove something else happened to the damaged appliances OP is going to be easy target for blame regardless, even if better design of the appliance would have saved it.
 
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