BURNT GROUND WIRE

[hooverdale]

Hello Everyone,

We have this situation on site where the ground wire of a submersible sump pumps were totally burnt out. (See attached photo)
Its a two (2) units submersible sump pump rated at 5HP, 400V, 3Phase, 3500RPM. Controlled by a Duplex type DOL controller 5HP, 400V, 3Phase.

The reason why the ground wire was burnt out is still unclear. We had the pump checked with our distributor and told us that one(1) unit of submersible pump was burnt out. While the other unit was still in good condition but they have to replace the entire ground wire.

We also found out that before the incident, the plumbing contractor was doing some welding works on the pumps discharge pipe because they added a flexible connector. And they had the welding ground attached on the discharge pipe. (See photo)

What do you guys think that caused the fault?

Thank you, Hooverdale

 

[itsmoked]

My first thought was, "classic lightning event". Then you mentioned the welding.. That could easily fry a smallish ground wire while welding. Major bone-head move in my in my UN-humble opinion.

BTW Your jpeg doesn't seem to work.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I suspect that the contractor did not have the welding ground attached properly to the discharge pipe. Just a few months ago I saw an extension cord destroyed when the ground wire became red hot from stray welding current.
The other possibility is that due to a poor installation and possibly open connections, when one motor failed the ground current somehow passed through both ground cables and the ground path impedance was too great to trip the protection immediately.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[hooverdale]

Thanks for your immediate response sir. Sorry about the jpeg. I'll try attached it again in pdf. (See file)

We had this reported initially to the plumbing contractor that the welding was the caused of the fault but their argument was " Why it doesn't happen to other sump pits?". Because they are also doing the same thing on other sump pits with the same duplex pump and controller.

I know its hard to analyze what happened with such little details. Can you guys help me where to start looking. Ill be your guy on-site

Thanks, Hooverdale

 

[waross]

Does this scenario fit the field conditions:?
The ground clamp was connected to one discharge pipe. Welding was done on the other discharge pipe. The lowest impedance ground path between the discharge pipes was through the ground conductor back to the panel and returning to the other discharge pipe on the other ground wire.
OR, from the look of the grounding site, the ground clamp may have been kicked of or somehow disconnected while welding current was flowing.
Not enough details. Have you checked the continuity and quality of the grounding conductors from the duplex panel back to the source?
(It's after 3:00 AM. I'm going back to bed. You should too Keith. GRIN)

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

I did Bill.

I think your scenario is right on. I also think the ground clamp came off or made a bad connection thru paint, as there is no other reason for the smoke damage around the clamping point.

Look! Even the cockroach is disgusted.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[SceneryDriver]

I've had to explain this to several welders. Just because you can strike an arc without the ground clamp present DOESN'T MEAN YOU SHOULD.

Hundreds of amps of welding current down a wire meant for 30A means that things start to smell funny pretty fast. A good ground connection while welding is a MUST.


SceneryDriver

 

[itsmoked]

I TIG weld. Forgetting the ground gets your attention VERY quickly. The instant you trigger the torch you realize there was no path for the ignition spike.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[hooverdale]

Hello Everyone,

Thank you for your response. I did a search on the sump pit and tried to find other clamping point but i haven't seen anything.

Have you checked the continuity and quality of the grounding conductors from the duplex panel back to the source?

The pump ground wire was tapped to the controller and it ends there.

as there is no other reason for the smoke damage around the clamping point.

I have no background on welding sir, is it normal for a clamping point to blacken like that? Is it a telltale that something went wrong?

The problem is the contractor are in denial and hesitant to admit anything. If only a cockroach could tell.

The ground clamp was connected to one discharge pipe. Welding was done on the other discharge pipe.

The discharge pipe pipe was connected at the top. (see attached - sorry about the picture quality. its a print screen, real file too big)

I think i will stick to the scenario that the grounding clamp was accidentally detached because it will answer their arguments "Why it doesn't happen on other pits?"..

Thanks, Hooverdale

 

[waross]

The blackening is evidence that either:
1> The ground clamp was removed while the current was flowing.
or
2> There was a bad connection, paint, corrosion, mill scale or other surface condition which created a bad connection.
A good welding ground connection may leave only a small spot about 1/4 inch in diameter or less and no blackening.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

And often NO mark at all.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[hooverdale]

Thank you Keith, Bill and Scenery. With the information gathered from you guys, i had it all written on my incident report.

Please read it and i'll be glad to hear any feedback.

See attached doc.

Thank you, Hooverdale

 

[itsmoked]

First paragraph: Change the word 'commonly' to 'infrequently'

Third to last paragraph repair -> repaired

I'd provide a clear tabulation of:

Hours
Labor rate
Total of service coast to repair
Material damage (pump repair/replacement)

And ask for compensation.

However, Ultimately work with them on it. Don't demand full payment or you will have an enemy service company and that helps no one.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[hooverdale]

Thanks Keith,

I coordinated with our pump distributor and asked them for a quote so i can have it attached in the incident report.

By the way, i forgot to ask is it allowed to conduct a welding works on a material with an electrical equipment connected to it? If so, what are the restrictions? Is there any rule/code that regulates it?

Thank you guys, as always you are very helpful.

Hooverdale

 

[hooverdale]

I did a revision on the report to make it more straight to the point that they shouldn't have done the welding with electrical equipment connected.

What do you guys think?

Thanks, Hooverdale