Being that electrical posts generate a lot of debate, I thought maybe I can do something constructive with all this knowledge. Here’s the question; my friend has an old Philco electric range and when he uses a pan with a metal handle and then touches the control knob both at the same time, he gets a shock. The appliance is wired three conductors and a ground. The control knob is a five position dial, I assume off, 0-110,110-110,110-220,220-220. The volts measured are from 0-40 volts. Sure baffled me. His solution is to use insulated handles. I know this is a dangerous situation. Either the elements or handles are insulated ‘hots’ and the other is the ground. Does anyone have any specific information to isolate the short? Thanks
Ken
Replies
Check for a loose, damaged or corroded neutral. More likely to be found close to the stove, the cord is a prime spot for faults, it could be located anywhere from the stove to the connections in the panel.
This is the sort of fault that got quite a few people hurt before the code was changed to require a separate ground. Redundant until it is needed to protect people it, a sound ground system, remains, contrary to Woody's ignorant protestations, a sound investment in safety.
the stove actually has a separate ground bonded to the frame in addition to the neutral. maybe the amperage trickling into the frame is not enough to trip the breaker?
Ken
Being as that the stove is connected by a three wire cord, as stated in your initial post, the ground wire you are looking at is likely just a jumper from the frame, metal body of the unit, to the neutral lug. A classic shared neutral situation. Don't confuse it with a true ground connection.
From your post I take it that you have a volt meter. Pull the stove out and remove the cover plate over the plug connections. A common fault is in the cord so it would be best to turn off the breaker to the stove before handling the cord. Wouldn't do to have you grab the cord and get shocked. Then, using a flashlight, closely examine all sides of the cord, especially where it cones out of the stove. Look for cracked or damaged insulation.
OK. With the cover plate off and the breaker on, be careful, check the hot to hot (H-H) and both hot to neutral voltages, A (Ha-N) and B (Hb-N). The results will be most informative.
I suspect you are going to find that the H-H will be close to 240v. Anything close, 220-250v, is pretty normal. The H-N voltages, A, B or likely both, are likely to be considerably less than 120v. This points to an inadequate neutral/ground. Find the fault in the neutral line and you will find the problem. Don't forget that cord, cord to stove and the connections at the range receptacle are all likely fault points. These connections get the most wear and tear. A loose , or weak, neutral at the panel or back to the transformer are also spots to check.
If you read a weak or unbalanced voltage triangle, 120-240-120 nominal, at the main feed and neutral, before the main breaker, the fault is upstream. The meter base, drop or even connections at the transformer could be involved. This, bad readings at the main lugs, H-N, would warrant immediate, most utilities will send out a truck to check this no matter the hour, attention from the electrical utility.
This major a problem is fairly rare so, without further information, I'm assuming the problem is somewhere between the range feeder connection at the panel and the cord connections.
Be careful and remember that a service call from a qualified electrician is cheaper than an ambulance ride. It also pays dividends in confidence.
" The appliance is wired three conductors and a ground."
I gathered that it to mean a 4 wire connection. However, the ground jumper might not have been removed from the stove.
But the other thing to remember is that the voltage difference is between two parts of the stove that should be be at the same potential, whether that is "ground" or "neutral".
Hmm. Missed that "and a ground part". That's what I get for posting without sleep.
"The volts measured are from 0-40 volts."
It is not clear where you measured this between.
There are two possible problems that I see.
First the knob could be hot, but I doubt it. But measure between that and a nearby ground. This is an old stove, but I don't know the age of the home so I am not sure if you have true ground outlets in the kitchen and also in older homes the water pipes are somewhat suspect until you know that they are properly ground and not being used as a ground them self.
But most likely the problem is that there is a fault in the "calrod" unit and the heating element is contacting the metal tube.
the voltage was measured between the trim around the knobs and a pan sitting on the elements. The voltage would vary according to which element the pan was sitting on and what setting the knob was on. So it was not just one element that was invlolved, but the highest voltage came from an element that looked like it was tamperd with. The cable supplying the range is new (3+- years) I believe running to a new subpanel on the third floor of an old house(new apartment).However, I don't know if the neutral was not bonded to the ground in the subpanel or what the rest of the system looks like.
Is it just that one trim ring or all of them?
I would start by pulling the stove out and measuring the voltage between the ground and neutral.
And also the ground to each hot.
Make these 3 measurements both with no burners on and then one on high.
I think that you might have a multiply error problem here, but hard to tell without seeing it.
You might have a missing ground or neutral connection in the stove. They might be reversed. and there might have been an internal wiring mistake inside the stove.
you are correct that it is a four conductor cable. I know the ground is bonded directly to the frame, but I don't recall whether the neutral is isolated from the frame or not. The trim ring is around all the knobs, I believe. I am unfamiliar with the term 'multiply error'. What is that?
Ken
That should have been multiple errors or problems.