Shock during fault

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Customer left a message on my phone yesterday about receiving a shock when starting a motor. Start/stop is via the push buttons mounted on a typical pump panel. I haven't been there yet, so details other then he seeing a flash, feeling a shock, and power being interrupted, is conjecture.

We pull EGs dang near everywhere so my thoughts are that the VD during the fault was still high enough for him to receive a shock. Would full sized EGs have helped?

30 HP, 480v, fuses @ PP, with older instantaneous breaker ahead of that. IIRC.
 
150811-0826 EDT

ptonsparky:

If I have two equal diameter wires of the same length, and at the far end I short them together, then the voltage drop on each wire is the same.

If one wire is the neutral or the EGC and it is grounded at the voltage source end, then relative to ground (earth) the far end point that is shorted together will be at a voltage potential of about 1/2 the source voltage relative to earth at the grounding point, and nearly the same at the far end.

If the source voltage is a 120 V RMS sine wave, then peak voltage is close to 170 V. Therefore, the peak voltage at the shorted end is 85 V relative to ground (earth).

Yes one would get a shock, and electronic components like RS232 and RS485 would be destroyed. This is why an RS 232 or 485 or 422 should include dielectric isolation in its path.

.
 
ptonsparky said:
View attachment 13146View attachment 13147

Moisture and hay dust on the HOA treminals eventually tracking to the metal of the switch. He managed to touch it while energized. Maybe next time he will call after it has blown 3 control fuses for "no reason". Maybe.
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Exactly the reason I stopped using switches like that in non-metallic enclosures. In fact, it is my opinion that the use of that type of switch in a non-metallic enclosure without a bonding jumper to the metal parts of the switch is a code violation.

I had often used A-B 800T devices in non-metallic enclosures until one filled with water and someone got shock when he touched the metal nut on the outside of the push button. With A-B 800T push buttons, if you connect a bonding jumper to the metal screw that holds the contact block in place, you have bonded all of the metal parts, so we started installing the bonding jumpers on the push buttons and selector switches, only to find out later, on a similar incident that bonding the contact block screw on a selector switch does not bond the rest of the metal parts like it does on the push buttons.

At that point I switched from the 800T series to the 800H series which are non-metallic devices and that eliminated the problem.
 
don_resqcapt19 said:
Exactly the reason I stopped using switches like that in non-metallic enclosures. In fact, it is my opinion that the use of that type of switch in a non-metallic enclosure without a bonding jumper to the metal parts of the switch is a code violation.

I had often used A-B 800T devices in non-metallic enclosures until one filled with water and someone got shock when he touched the metal nut on the outside of the push button. With A-B 800T push buttons, if you connect a bonding jumper to the metal screw that holds the contact block in place, you have bonded all of the metal parts, so we started installing the bonding jumpers on the push buttons and selector switches, only to find out later, on a similar incident that bonding the contact block screw on a selector switch does not bond the rest of the metal parts like it does on the push buttons.

At that point I switched from the 800T series to the 800H series which are non-metallic devices and that eliminated the problem.
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Typical "pump panel" probably has a metal cabinet. But I always thought those style switches were not designed all that well to ensure the switch body was well bonded even when mounted in a metal enclosure, nothing there to scratch through the paint like there is with a conduit/fitting locknut.
 
kwired said:
Typical "pump panel" probably has a metal cabinet. But I always thought those style switches were not designed all that well to ensure the switch body was well bonded even when mounted in a metal enclosure, nothing there to scratch through the paint like there is with a conduit/fitting locknut.
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The picture of the enclosure where the buttons came out of looked to be non-metallic at first look, but on a second look, the wall looks too thin to be a non-metallic enclosure.

Allen Bradley has a bonding bracket (800T-N300) for the purpose of bonding the metal parts of the selector switch or push button to the metal enclosure, but I have never used one. I believe it is required for CSA listed equipment used in Canada.
 
Why hasn’t the grounding terminal been used? I’ve been using CH (Brookhurst originally) for 40 years, never had a problem with them. The sealing washer can cause problems with a powder coated steel enclosure as the metal body is insulated from ground. CH make a box spanner to fit the bezel to tighten them in to the plate.

When I first used them the seal was cork not rubber as now.
 
Tony S said:
Why hasn’t the grounding terminal been used? I’ve been using CH (Brookhurst originally) for 40 years, never had a problem with them. The sealing washer can cause problems with a powder coated steel enclosure as the metal body is insulated from ground. CH make a box spanner to fit the bezel to tighten them in to the plate.

When I first used them the seal was cork not rubber as now.
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I have been using CH for the most part of 30 years and I do not remember anyone being shocked because of this problem. Generally I get called when the 1st control fuse blows, not after the 3rd time and a shock. The 4th fuse blew right away but by then he was using a screwdriver to push the Start. Pain is a good teacher.
 
ptonsparky said:
I have been using CH for the most part of 30 years and I do not remember anyone being shocked because of this problem. Generally I get called when the 1st control fuse blows, not after the 3rd time and a shock. The 4th fuse blew right away but by then he was using a screwdriver to push the Start. Pain is a good teacher.
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Seems to be typical for any make of that style switch. Rubber sealing washers inside, smooth legend plate outside, nothing scratches into the paint to ensure a good bond to the enclosure.

Also typical for pump panels - control circuit tapped to supply voltage with no overcurrent protection other then maybe 100 amps plus on 16-14 AWG control leads.
 
As you say the legend plate makes a good insulator even though it’s not supposed to be.

Unless CH have altered the design since I retired there was a cast connection for earthing which we always used as our panels were lacquered aluminum. With the seal, legend plate and the lacquer the mounting bezel was pretty well insulated from earth, any damp, etc and the operator got a belt if the earth connection wasn’t used.

You could get a waterproof rubber boot that replaced the bezel, I don’t know if they’re still available. They used to go all gunky after a while and fall apart.


“Pain is a good teacher.” So is a punch on the nose from an irate plant operator that’s just had 110V up his arm. :cry:
 
Tony S said:
As you say the legend plate makes a good insulator even though it’s not supposed to be.

Unless CH have altered the design since I retired there was a cast connection for earthing which we always used as our panels were lacquered aluminum. With the seal, legend plate and the lacquer the mounting bezel was pretty well insulated from earth, any damp, etc and the operator got a belt if the earth connection wasn’t used.

You could get a waterproof rubber boot that replaced the bezel, I don’t know if they’re still available. They used to go all gunky after a while and fall apart.


“Pain is a good teacher.” So is a punch on the nose from an irate plant operator that’s just had 110V up his arm. :cry:
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Rubber boots are still available for most makes out there. They seem to wear holes in them rather fast and next thing you know you still have exposed metal body somewhere in the hole, some are worse then others depending on design, even different types for same product line.

I have never seen a bonding fitting for such devices. Even the pump panels like OP has - those switches are factory installed in the pump panel with no kind of bonding fitting.
 
CH-PB-D.jpg
This I find very strange, I can’t see an international company like CH having two different patterns.

The arrow points to the earth terminal on the ones I’ve been using for forty years.

BTW, they were originally made by Brookhurst Switch Gear. Originally the connections were square and not angled as the modern ones. You can imagine the performance trying to disconnect a terminal in the middle of a stack of blocks.
 
Tony S said:
View attachment 13159
This I find very strange, I can’t see an international company like CH having two different patterns.

The arrow points to the earth terminal on the ones I’ve been using for forty years.

BTW, they were originally made by Brookhurst Switch Gear. Originally the connections were square and not angled as the modern ones. You can imagine the performance trying to disconnect a terminal in the middle of a stack of blocks.
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There is actually a screw for an EG conductor?
 
ptonsparky said:
There is actually a screw for an EG conductor?
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Yes, I naturally assumed all CH gear would be to the same pattern. Everything else in that range is interchangeable.
That’s the thing I can’t understand, why have two different patterns for basically the same product????

That is the standard pattern fitted on all the plants I’ve worked on.

I started in quarrying so conditions were normally damp and quarry operatives on the large and burly side, 110V up their arm and they wouldn’t be happy. Hence my comment about a punch on the nose, it happened, but it wasn’t me that got the punch ;-)

I then moved in to an iron works. That’s where I came across the lacquered aluminium operator desks. Without the connection the body of the PB would be effectively isolated from earth. Iron dust gets everywhere so earth faults were quite common. Foundry men tend to be large and bad tempered.
We had one episode where the earth had become disconnected. With every PB on the panel linked but isolated from earth every PB gave you a belt.


It took me ages to find that picture in the CH catalogue, I was on page 100+ and thinking I’ve been hallucinating for the past 40 years. If I was hallucinating, where did all that earth (EG) wiring go?
 
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