Zero Potiential Testing at the Local ON-OFF Switch

[TVH]

Gents:
Would appreciate your comments on the following questions:

An electrical pump at a water treatment facility has a local on/off switch. The main switch is located in the neary electrical substation. A permit has been issued to work on the electrical pump. The main swith in the substation was subsequentely isolated by a lock and tag applied by the substation supervisor and a lock and tag applied by the craftsman working on the electrical pump. All in order.

Before work commences on the electrical pump a zero potiential test is required.
Is it acceptable practice to try to start the pump at the local on/off switch to verify zero energy potential or is another electronic test required? If another electrical test is required then why and where should the test be conducted?

Regards,
TVH

 

[Smart $]

...
Before work commences on the electrical pump a zero potiential test is required.
Is it acceptable practice to try to start the pump at the local on/off switch to verify zero energy potential or is another electronic test required?

NO... if any work on the electrical portion of the system is to be performed. Reason being, switches and/or other equipment can be defective and fail to perform as normally expected.

If another electrical test is required then why and where should the test be conducted?

Depends on the scope of work, which you failed to elaborate on. If any work on the electrical, de-energization is typically confirmed with a live-dead-live test on otherwise energized conductors or respective terminals or bussing, wherever initial access to energized parts of the system are exposed, but could also be preemptively required on the load side of the disconnecting means. The actual details of the procedure should be contained in the company safety program documentation.

 

[Jraef]

...
Is it acceptable practice to try to start the pump at the local on/off switch to verify zero energy potential or is another electronic test required? ...

And no, this is not a valid test of zero potential. Unless you are talking about a 115V single phase motor, you could have one conductor left at full potential and the pump would not start, but a worker coming in contact with it could still get killed. If it is a 115V single phase motor, you could in theory have a ground potential difference on a Neutral that could be lethal under the right circumstances.

The only valid test is a Zero Potential test. Remember the "Old or Bold" saying? If you have never heard it...

"There're are Old Electricians, and there are Bold Electricians, but therer are very few Old Bold Electricians."

 

[cdevine]

A permit has been issued to work on the electrical pump.

Firstly, I assume you mean electrical work on the electrical pump (live-dead-live check required) rather than non-electrical work on the electrical pump (effective isolation test required. Not necessary to do live-dead-live check)

The main switch in the substation was subsequently isolated by a lock and tag applied by the substation supervisor and a lock and tag applied by the craftsman working on the electrical pump. All in order.

Secondly, the main switch in the substation is the isolation point. Its correct function is what should be verified at the same time as placing the lock and tag. OSHA drives this requirement. That is, a live-dead-live test may be performed at the switch in the substation or perhaps a try start is commonly performed to prove an effective isolation. There are practical and safety issues associated with both of these test methods. This is why voltage indicator LEDs with self test capability make a lot of sense.

Before work commences on the electrical pump a zero potiential test is required.

Thirdly, in the case of electrical work, yes another live-dead-live is required at the motor terminals before coming into contact with them. This is an electrical code requirement.

Is it acceptable practice to try to start the pump at the local on/off switch to verify zero energy potential or is another electronic test required?

Its never acceptable practice for electrical work. Its acceptable practice for non-electrical work but far from best practice.

If another electrical test is required then why and where should the test be conducted?

In summary, best practice verification steps for electrical maintenance should be IMHO:

1. Verify at switch in substation at the time of lockout tagout using voltage indicator LEDs with self test capability
2. Verify at motor terminals at the time of work using live-dead-live check

And best practice verification steps for non-electrical maintenance should be IMHO:

1. Verify at switch in substation at the time of lockout tagout using voltage indicator LEDs with self test capability
2. Verify at motor using try start. Not conclusive by itself but may identify locking out of incorrect switch in substation

The often forgotten aspect is to verify what you are locking not just the equipment you are working on. The equipment you are working on may not be operational or energised during try start for other reasons that are temporary eg wrong control mode, siezed impeller/shaft. These temporary reasons for non operation may disappear while maintenance is taking place and could result in serious injury.