Temporary Installation Headache

[Stephen Jay]

Hi 

Im currently in the forces and employed as a sparky, we currently use a system call LAPDS made by a company called blakley, when it comes to inspection and testing we have a headache.

so, we use a generator as source, then distribute 3 phase down through modules to single phase to a final module that will have either 16 amp iec sockets or weatherproofed 13 amp sockets,

the cables are all made by us and pat tested by us, the modules are all inspected by us as per the manufactures instructions as is the generator. The modules all have either 63, 32 or 16 amp RCD/RCBO circuit breaks on there outputs.

Before we do anything we fully design the system producing a full area plan to scale showing where every cable and module is laid and then a linear plan showing the full connectivity of the plan, as well as this we also work out, for every cable:

Design current, protective device, Voltage drop, Zs max, Zs, R1/R2, Pfc, cable burn out time, min CPC size,

It is then cabled together as per the plan, then all final distribution is RCD tested recording all the trip times

Do we require to carry out anything else to make sure we are on the correct side of the law

any advice would be helpfull

regards

steve

 

[Andy™]

along with testing trip times, you would need Zs

have a look at BS7909. designed more for entertainment temp power, but its pretty much exactly what you are doing

 

[Stephen Jay]

BS7909 is the way we are going,

one area we are unsure of is the Zs, when we record it, are we right to say it has to be by test and not just by calculation

 

[Andy™]

you can only do Zs by calculation if you have measured Ze & R2

 

[Stephen Jay]

When we work out our cable calcs

we use the Ze of the genset from our genset hand book, then the R1/R2 of the cable from the table in the onsite guide to give us the Zs

 

[Andy™]

unless you actually measure either Zs or R2, how do you know there isnt a broken earth somewhere along the line, or do you wait until someone is dead?

 

[Sidewinder]

Welcome to the forum Stephen, as Andy says, you need to make measurements somewhere to confirm your installed readings against your calculated ones.

Measuring R1 & R2 then adding them to Ze is a valid way of fgetting a Zs.

However, how can you look up the Ze value?

Your gensets are mobile/portable/transportable?

So, they provide you with a TN-S supply?

The earthing at the genset is an earth rod, fitted when the generator is sited?

 

[Stephen Jay]

1. Hi thankyou for the advice, and no we we dont wait to kill someone, i missed of something about our system
2.  
3. we have what is called a PCLM, (protective conductor loop monitor) it starts from the genset and uses a second seperate earth spike, this is then transported down the cables with a pilot wire, should a cable be disconnected , or cut or damaged  then the protection device before the cable operates cutting off the supply, therefore it is impossible to turn on a circuit breaker to a socket that is not connected to the next module, ie the cable has to be connected at both ends before the PCLM will allow the circuit breaker to be turned on.
4. The exception to this is the final module output which is a standard 16 amp iec socket which is fitted with a 16 amp RCD,

Thanks for the advice and i think it probably in our best interest to measure the Zs as well regardless