DC / 110 Volt EM lighting

[Hilly]

Few questions about an existing static inverter system we are upgrading.
1. Distribution has to be DP - why, where can you find reference
2. From the inverter to the existing DB no cpc has been run with the tails, to me this looks like a glaring oversight or have i missed something.
3. Testing. If you go to the extremity of a circuit and decide to put yourself across the live conductors you would know, on that basis surely some live testing is called for. Here is the rub. How can you measure ZS when the earth loop path dosent exist. Would a list of R1 + R2 be appropriate. Do any disconnection times have to be met on these systems.

questions questions

Regards in advance

Hilly

 

[johnnyb]

Could you not run a flying lead out, say a piece of singles, null the lead on your meter and then test R1.

 

[Hilly]

johnny,
could do mate but to what end? system is already energized as it is existing so the fact that the last fitting is lit proves R1, dont know what i would do with a reading if i took it. more concerned with lack of cpc at DB. Thanks for giving it some thought though mate. Replies are a bit thin on the ground.

 

[Guest123]

Hilly,

Have you measured the Zs at the DB?? to confirm there definately isn't an earth present.

 

[Hilly]

Len,
couple of issues here. first the sytem is installed in micc / steel conduit in the slab so iam sure there will be an earth present somehow but i dont think its the correct way to acheive it. also like i said earlier does an earth fault path exist on an inverter / battery system and if so what meter would measure ZS on 110v DC certainly not my fluke. Many thanks for any thoughts. ps the engineer who we are working for is equally as clueless as moi.

 

[johnnyb]

Sounds to me its an old system thats never had a recognisable cpc as in an actual earth cable as such.
They used to rely on the conduit or outer copper of the micc as an earth in days gone by, so i think thats the reason, its never been there.
Or Hilly i am missin the plot and i can,t understand what you are on about.

 

[Hilly]

John,
The latter i think! but it is my descriptive skills at fault. The DB is fed by 16mm 6491x in plastic copex FROM the static inverter. so even though there is probably an earth introduced via the micc/conduits there isnt one from the source. my question originally is why the installers left it out, am i missing something.

 

[johnnyb]

Got ya mate, yeh fully understand now, i think its a mistake on the installers of the inverter and yeh i think you are right it sure should have one.
I thought it was a conduit feeding the inverter sorry mate.

 

[Guest123]

Hi Hilly.

I just need you to clarify a couple of things for me as I'm getting more and more confused, sorry.

Your inverter system, is it a back up for em lighting, vital systems etc fed via a large battery installation??

If so is it on an auto changeover in the event of mains failiure?? if so I'm guessing there is a mains supply at this dis board too??

Or am I barking completely up the wrong tree?? I've been researching your query for quite a while but end up more and more confused.

Thanks.

 

[Hilly]

Len,
Yes mate correct on both accounts. sort of. static inverters convert mains voltage to DC so for instance if you have a maintained system, on mains failure the luminaires are supplied from the batteries with no discernable loss of power ( apologies grandma / eggs ). so yes there are phase failure relays for auto change over but the mains supply goes to the inverter and the supply to the DB is 110v from the inverter. Hope this is a bit clearer.If not please accept as an excuse the northern tradition of boozing on a sunday afternoon handed down by my father and his father before him.
Regards, Hilly