UK Which one is not a characteristics of the supply?

Learner96 · Jan 17, 2022

Prospective short circuit
Prospective fault current
Ze
Zs
Kinda got stuck at this question and not sure wich one of these is the right choice. Please help me,thank you.

pc1966 · Jan 17, 2022

I would guess it is Zs, as that might depend on local bonding providing parallel earth paths.

So while is a characteristic of the supply, it is not wholly of the supply.

pc1966 · Jan 17, 2022

However, you could also argue the value for "PFC" recorded for an installation would be the higher of the measurements of PSCC (independent of earth) and the PFC in to actual Zs (allowing for lower than Ze so higher possible fault current) to decide if the breakers, etc, are up to interrupting it.

So not really a very well-worded question!

timhoward · Jan 17, 2022

It's not a great question.
The first two can apply anywhere within the installation, including the supply. So it can't be then.
Ze can only apply at the supply origin. So it can't be that.
Zs incorporates the Ze at the origin when you measure it, or calculate it using Zs=Ze+(R1+R2). I think they are getting at the fact that a component part of it is always the supplies earth loop impedence (Ze) so it is more than just the supply.

So the first 2 can apply to the supply. The 3rd must apply to the supply.
The 4th can't only apply to the supply as that would be Ze.

ipf · Jan 17, 2022

There's one relating totally to external value.......and one which doesn't, being additional to it.

To OP..... which one?

catdog1121 · Jan 17, 2022

I would say Zs as that is not a measurement at the supply, it takes into account both the supply and the circuit so you would have multiple Zs readings for each circuit where as the others are measured at the supply..

Wing_na_Prayer · Jan 18, 2022

Learner96 said:
Prospective short circuit
Prospective fault current
Ze
Zs
Kinda got stuck at this question and not sure wich one of these is the right choice. Please help me,thank you.

Zs- as this is the earth loop at the final circuit. Zs is the total of Ze + R1 & R2. All the others are applied to the supply.