Maximum zs generator and rubber box

UPS · Apr 3, 2018

Can anyone point me in the right direction.

I am working for a company who do temp power for welders etc from a generator.

We have been given a load of new boards to pre check befor they go on site. Powerlock connectors in and then D63 on a commando sockets.

I have put the maximum zs of the sockets from the table I usually use. But have just recieved an email from a member of management saying that we need to discuss the max zs values I have used (0.14).

Am I missing something?

Risteard · Apr 3, 2018

UPS said:
View attachment 41625

This is the value I have from the generator this doesn’t seem dissimilar from what I would expect from a fixed install.

That doesn't mean that the generator can actually physically deliver that current into a fault though without the voltage collapsing and the generator stalling. Of course you will have a low impedance to the neutral/Earth link in your own generator - still doesn't mean the generator can provide that fault current.

westward10 · Apr 3, 2018

I disagree this is one of the key features of a PMGenerator, sustained output even under fault conditions.

Wilko · Apr 3, 2018

Hi - the meter shows calculation from the measured impedance and V. It doesn't reflect the stored energy in the generator flywheel which would be important if the current was required for 5 seconds, say. IMHO

davesparks · Apr 3, 2018

westward10 said:
PM Generators have been proven to sustain short circuit current during fault conditions which prevents the field collapsing.

Not something I’ve ever come across yet, presumably PM = permanent magnet?

Surely the engine is still going to need time to react to the change in load though?

davesparks · Apr 3, 2018

UPS said:
View attachment 41625

This is the value I have from the generator this doesn’t seem dissimilar from what I would expect from a fixed install.

On a generator that value is not much use, that meter calculates the value it doesn’t measure it. It doesn’t take in to account any of the characteristics of the alternator or the engine.

UPS · Apr 3, 2018

davesparks said:
On a generator that value is not much use, that meter calculates the value it doesn’t measure it. It doesn’t take in to account any of the characteristics of the alternator or the engine.

So how do I know that I am going to achieve disconnection times required?

davesparks · Apr 3, 2018

UPS said:
So how do I know that I am going to achieve disconnection times required?

You’ll need to characteristics of the generator to establish the available fault current by calculation or from the data sheet for the generator.
For all the generator setups I am involved with I use variable earth leakage relays to achieve fault protection.

LeeH · Apr 3, 2018

I’m going to embarrass myself here and ask what a rubber box is.

?

Great posts from Davesparks btw.

UPS · Apr 3, 2018

LeeH said:
I’m going to embarrass myself here and ask what a rubber box is.

?

Great posts from Davesparks btw.

Just like a waterproof box with sockets mounted on it.

[ElectriciansForums.net] Maximum zs generator and rubber box

davesparks · Apr 3, 2018

LeeH said:
I’m going to embarrass myself here and ask what a rubber box is.

?

Great posts from Davesparks btw.

Rubber box is a company who manufacture distribution units (usually referred to as distro) for temporary installations, usually made of tough rubber.
The term rubber box has come to mean any rubber distro, much the same as vacuum cleaners being referred to as hoovers.

shaun1 · Apr 3, 2018

davesparks said:
You’ll need to characteristics of the generator to establish the available fault current by calculation or from the data sheet for the generator.
For all the generator setups I am involved with I use variable earth leakage relays to achieve fault protection.

Out of interest, how do you protect against Line to neutral faults?

Maximum zs generator and rubber box

UPS

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Risteard

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westward10

Wilko

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davesparks

davesparks

UPS

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davesparks

LeeH

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UPS

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davesparks

shaun1

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