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Post by cablehack on Aug 24, 2019 12:02:17 GMT
I figured though, grounds and neutrals are bonded in most electrical panels anyways so it should be the same right? Well, I got some more interesting results. While it's true that neutral and ground are connected together in the fuse/breaker box, don't be surprised to find the neutral showing a few volts above ground when you measure at an outlet. The reason for this is because there will be voltage drop along the neutral conductor depending on the loading. This is actually what you're measuring. Since the ground conductor does not have any current flow (except in a fault condition) then there is no voltage drop across it. |
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Post by ckfan on Sept 1, 2019 22:27:45 GMT
David (turbokinetic) came over to visit Travis and I this weekend. I really enjoyed learning from him. I always learn a lot of good things. He helped me do the light bulb test described earlier in this thread. We tested for leakage current from the base to hot and neutral. We got about 14mA. So that confirms that there is a ground fault in this unit that is more than what is “acceptable”. So my current plan after talking to him is to put a grounded cord on it to bleed off this leakage current and then put it on the cabinet for a few months to test it and see if it survives and stays consistent or gets worse. We will see what happens! The only problem I will have is that I don’t have any grounded outlets in my house! Would it be acceptable to mark the hot and neutral on the line cord and then tie the chassis to the neutral instead of a proper ground?
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Post by turbokinetic on Sept 4, 2019 2:42:57 GMT
David (turbokinetic) came over to visit Travis and I this weekend. I really enjoyed learning from him. I always learn a lot of good things. He helped me do the light bulb test described earlier in this thread. We tested for leakage current from the base to hot and neutral. We got about 14mA. So that confirms that there is a ground fault in this unit that is more than what is “acceptable”. So my current plan after talking to him is to put a grounded cord on it to bleed off this leakage current and then put it on the cabinet for a few months to test it and see if it survives and stays consistent or gets worse. We will see what happens! The only problem I will have is that I don’t have any grounded outlets in my house! Would it be acceptable to mark the hot and neutral on the line cord and then tie the chassis to the neutral instead of a proper ground?
As always it was good to visit you guys! Glad to show you some of the ways I check out and fix these old machines, as well.
There's only one way to know if it is stable, or failing rapidly and that is to give it a nice, long test run.
As for the grounding, attempting to bond the cabinet to the neutral would probably make the problem (shock hazard) worse. It is true that the neutral and ground do both go back to the same point on the transformer. The problem would happen when there was a corroded pin on the plug, loose contacts in the outlet, or a broken wire. Then, the entire cabinet would become very much live, with enough current potential to run the compressor motor.
If you want to go to the expense of using an isolation transformer, that would be an option, however the transformer's core and shield still needs proper grounding to ensure isolation.
Sincerely, David
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Post by ckfan on Sept 4, 2019 16:09:27 GMT
Thank you for that information. I figured that connecting the base to the neutral would be a no no but I wanted to make sure. So it sounds like I need to run my own ground line in order to make it safe which will be a pain if it ever finds it’s way into the kitchen. Could you explain what you mean about grounding the isolation transformer? I thought the whole point of that was to isolate the power from the main feed in order to prevent a shock.
There is also a possibility that I could run a ground line to a water pipe which would be easy to do. I have seen that done before but looking online shows that some people are wary of doing it that way. The way I figure, it should be a great ground and should have enough metal to dissipate the energy should a short circuit ever occur. What do you all think?
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Post by turbokinetic on Sept 5, 2019 12:01:43 GMT
Thank you for that information. I figured that connecting the base to the neutral would be a no no but I wanted to make sure. So it sounds like I need to run my own ground line in order to make it safe which will be a pain if it ever finds it’s way into the kitchen. Could you explain what you mean about grounding the isolation transformer? I thought the whole point of that was to isolate the power from the main feed in order to prevent a shock. There is also a possibility that I could run a ground line to a water pipe which would be easy to do. I have seen that done before but looking online shows that some people are wary of doing it that way. The way I figure, it should be a great ground and should have enough metal to dissipate the energy should a short circuit ever occur. What do you all think? Hi Ray; good morning! Sorry about the confusion about the isolation transformer. You're right the secondary side is to be non-grounded. There is, however, an iron core, as well as shielding inside the transformer. This is in place to prevent capacitive leakage from the primary to the secondary; as well as if the transformer winding fails, mains power can't short circuit to the secondary side. So if you don't use it, and power the transformer from a 2-wire cord, it would work but the safety factor would be greatly reduced. I don't know what to think about the water pipe grounding. Would completely depend on the design of the water plumbing; especially the bonding of the pipe around any non-metallic compoments such as a water meter. I would say this method could work, however it would require testing to be sure it was adequate. Sincerely, David |
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Post by ckfan on Sept 5, 2019 19:43:52 GMT
Thank you David, that makes sense about grounding the primary side of the transformer. What kind of test would you suggest for making sure the water pipe ground is sufficient? I definitely don’t want to use something inadequate.
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Post by turbokinetic on Sept 5, 2019 20:00:21 GMT
Thank you David, that makes sense about grounding the primary side of the transformer. What kind of test would you suggest for making sure the water pipe ground is sufficient? I definitely don’t want to use something inadequate. I'm not sure what sort of specification would apply to a ground, via a water pipe. I would want to see a very low resistance (measured with a multimeter) between the pipe and a Neutral point in the electrical outlet. As to what is adequate, that's up for debate. If it were in the single digits of ohms it should be adequate; however the performance if there were actual fault current through this path is what worries me. |
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Post by ckfan on Sept 6, 2019 3:01:30 GMT
Thank you David, that makes sense about grounding the primary side of the transformer. What kind of test would you suggest for making sure the water pipe ground is sufficient? I definitely don’t want to use something inadequate. I'm not sure what sort of specification would apply to a ground, via a water pipe. I would want to see a very low resistance (measured with a multimeter) between the pipe and a Neutral point in the electrical outlet. As to what is adequate, that's up for debate. If it were in the single digits of ohms it should be adequate; however the performance if there were actual fault current through this path is what worries me. Right, that’s what worries me too. I lived in an old house before that had grounded outlets...sort of. They all had tiny wires (like 24 gauge) going to water pipes nearby. I can’t imagine what would happen in a dead short scenario. I guess the wire and pipe could have the potential of becoming a heater! |
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Post by coldspaces on Sept 6, 2019 3:20:44 GMT
They used to ground to the metal water pies. Not sure it is code anymore. Of course you need metal water pipes in the house and feeding it. And as said jumpers around plastic meters and such.
My grandfathers good friend had a jumper around his meter. He needed to disconnect it to do some plumbing. When he did it started to draw a arc he put it back and found his house had lost its neutral. Fortunately he understood what was going on and didn't keep disconnecting it. Not sure if his main box was grounded to the water pipes or what.
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Post by elec573 on Sept 7, 2019 6:25:26 GMT
Hi Ray
‘Haven’t been on in a while I could answer your basic questions however.
The nec requires 2 -8’ ground rods I believe 6’ ft apart for a service entrance .
Its number 6# for 100 amp service and number 4 for 200 amp service.
And yes it’s required to bond the water meter (meaning it’s clamped on both sides of the meter) in case the water meter was removed.
But that’s back when everything had metal or copper piping.
At one time you were required to take a ground out to a well casing and bond it there .
But as far as outlets you can just run a ground wire (insulated green number 14 ) back to the panel .
But when a dr is leaking to ground we all know what that means (sorry)
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Post by ckfan on Sept 7, 2019 11:49:31 GMT
Thank you Herb. I think at this point it makes more sense to get an isolation transformer and just ground the primary side of it. In my mind it would be much kinder to the motor since it wouldn’t constantly be passing current through the bad section of winding to ground.
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