Earthing of Three phase Motor

[7upsgreat]

The braiding of your bog standard S/Y you could pick up at your local wholesalers is a screen not an earth, it is no to be used as an earth but should be earthed itself (low voltage applications), S/Y is a type of cable design and strictly speaking saying it cannot be used as an earth is incorrect, it comes down to how it has been design and manufactured, there are S/Y's that are suitable for the braiding to act as the earth, however, these are not the S/Y's we can pick up in any wholesaler.

S/Y, C,Y and Y/Y are how a cable construct is arranged and many manufacturers out there have their own specific versions with their own individual design and environmental tolerances.

Accepted Darkwood, that wasn’t my question. Where I’ve seen it installed the CPC has always been a separate dedicated core. My query was regarding Robs statement that it wasn’t compliant in a Ex environment. I just simply wanted clarification of this and where/what regs precluded it’s use.

 

[Bobster]

Accepted Darkwood, that wasn’t my question. Where I’ve seen it installed the CPC has always been a separate dedicated core. My query was regarding Robs statement that it wasn’t compliant in a Ex environment. I just simply wanted clarification of this and where/what regs precluded it’s use.

It's product standards and cable glands do not meet what is required to be used as an exd cable. Could be used in Exe situations, but as you know a 3ph motor cant comply with this type of design.

 

[timbobelfast]

Standard practice in hazardous areas is 3 core swa or braided bfou cabling with the motor frame tied to local earth at the skid earth boss. Perfectly acceptable, and Zs values for fuses are checked during initial inspections.
It can be hard to calculate expected continuity readings when parallel earths are used this way!

The braid or swa is obviously tied down at the mcc side in the switch room etc.