Earth Loop Impedence

[Anwar Pasha]

Recently, a client hired an electrical consultant to inspect one of the installation. The installation was done as per codes and standards but the problem is after inspection consultant claims to have observed high earth loop impedence. My question is whether it is a stipulated norms as per NEC??? how essential is this needs to be carried out?? I had not seen any such remarks in design drawings stating anything about loop resistance.

 

[T.M.Haja Sahib]

I do not think earth loop impedance has any thing to do with NEC. The earth loop impedance is important in those electrical installations outside the US in which the EGC is not bonded to the neutral conductor at the service equipment but is grounded separately from the neutral.

 

[Besoeker]

I do not think earth loop impedance has any thing to do with NEC. The earth loop impedance is important in those electrical installations outside the US in which the EGC is not bonded to the neutral conductor at the service equipment but is grounded separately from the neutral.

Section 605 of BS7671 applies.

 

[T.M.Haja Sahib]

Bes:
The question is what kind of protection kicks in when there is a break in the incoming service neutral in an electrical installation with TT or TN type of protection and what role the earth loop impedance plays in each.

 

[Phil Corso]

T.M...

The simplest for 3-ph is Negative Sequence!

Regards, Phi Corso

 

[T.M.Haja Sahib]

The simplest for 3-ph is Negative Sequence!

Thanks, Phil. But I think your suggestion is for equipment protection and not for protection of life in which case multiple grounding of neutral at pole locations may help reduce touch or step potential at the service equipment, when there is a break in the incoming service neutral to that service equipment.

 

[Besoeker]

Bes:
The question is what kind of protection kicks in when there is a break in the incoming service neutral in an electrical installation with TT or TN type of protection and what role the earth loop impedance plays in each.

Most of the systems here are TN-S which has a separate PE conductor.
The earth loop impedance has a maximum impedance which depends on the rating and type of protection device. Obviously, the higher the rating of the protection device, the lower the maximum earth loop impedance.
Loss of the neutral on a three phase system would probably fry some single phase loads.

 

[T.M.Haja Sahib]

The earth loop impedance has a maximum impedance which depends on the rating and type of protection device. Obviously, the higher the rating of the protection device, the lower the maximum earth loop impedance.

Does not the above apply only to TT system and not TN-S system? Please quote with BS regulations, if possible.

 

[Besoeker]

Please quote with BS regulations, if possible.

I already did.
Section 605 of BS7671.

 

[T.M.Haja Sahib]

Bes:
While for TT system, the size of over current device depends on earth loop impedance in an electrical installation, the same does not hold for TN system. Otherwise NEC would have had rules on it.

 

[Besoeker]

Bes:
While for TT system, the size of over current device depends on earth loop impedance in an electrical installation, the same does not hold for TN system. Otherwise NEC would have had rules on it.

BS7671 is not NEC.

 

[T.M.Haja Sahib]

BS7671 is not NEC.

Yes. It is broader in scope, I think. It permits TT, TN protection systems, where as NEC permits only a specific sub set of TN protection system and so there is no place for earth loop impedance in it.