Maximum Zs clarification

[Jona Zeolla]

One of my clients asked me if there was a maximum Zs value when it came to testing the Main incoming supply of a TN-S system, as i'm not fully sure my gut instinct was that it depended on the type of system.

Can someone assist me?

 

[i=p/u]

depends on the system there is a value for each

 

[HandySparks]

depends on the system there is a value for each

i=p/u,
Which, for TN-S, is...

 

[MarkieSparkie]

One of my clients asked me if there was a maximum Zs value when it came to testing the Main incoming supply of a TN-S system, as i'm not fully sure my gut instinct was that it depended on the type of system.

Can someone assist me?

Typical 'maximum' Ze values are TN-S 0.8Ω and TN-C-S 0.35Ω, however, these values are not guaranteed by the DNO who may provide supplies with higher values for operational reasons in exception circumstance.

 

[Deleted member 26818]

The maximum value will also depend on the protective device used to protect the supply.
The maximum Ze for a 100A supply would be less than 0.4Ω.
A Ze of 0.8Ω would limit you to a supply somewhere between 45-60A depending on the protective device.

 

[Engineer54]

The maximum value will also depend on the protective device used to protect the supply.
The maximum Ze for a 100A supply would be less than 0.4Ω.
A Ze of 0.8Ω would limit you to a supply somewhere between 45-60A depending on the protective device.

I wonder how many electricians consider this limitation when conducting their installation tests?? More to the point, would a 19 day DI even be aware of the limitation??

 

[Jona Zeolla]

Thanks guys really helpfull infomation...much appreciated