Testing DC circuits

[Guest 004]

Hi

I have been asked to test some DC circuits. Which are emergency lighting circuits. Has anybody had any experience of this? Never seen a DC loop meter?

 

[spark 68]

In general, the DC side of things are usually kept completely seperate electrically from the AC side, so you would test these seperately, they are likely Isolated fom earth via transformer/PSU and either an inverter and/or battery.

You probably won't need to test the DC side to earth (as in loop wise), but some more details on what exactly you are testing, and testing for, would be helpful.

 

[Guest 004]

These are two boards that I have to test. Basically the emergency lighting has ac and dc supplies, which are separate inside the fittings. The boards have a constant 230 dc supply, which supply final circuits via a relay, which is connected to the AC supply. So when the AC drops the relay flicks over to the DC contacts, thus energising the dc side of the lights.

 

[Guest 004]

Anyone?

 

[Engineer54]

Anyone?

You'll only need to carry out IR testing on these circuits. If you want/need to go further, continuity tests
could be carried out, also check on volt drop at the extremities of these circuits.

 

[spark 68]

I wasn't sure enough on this type of system to give a definitive answer E54.

I suspected maybe just an IR and continuity tests, assuming part of the DC side is not tied to earth.
But as I said, I have no experience of this type.

Most battery backed systems I have seen/worked on, have been of the UPS type, and as such were just tested as normal AC systems.
Except for the backup part and unit, the ATS and distribution side being conventional.

The other type being ELV (12, 24,30,48 and 110 V DC)

I have never seen the DC being used at this voltage (230V) and taken to the accessory directly as is.

Iam always wary of DC at this sort of voltage, and big batteries.

 

[Guest 004]

OK thanks guys. The install is indeed unique, and quite possibly the first and maybe only one. It is a government building, which forms part of a Nuclear bunker. Interesting to note, that it has a generator back up as well. So the DC kicks in, whilst the generator kicks in. We have dropped the AC side of things for a whole weekend, and the lights are still working on batteries the following Monday.

So it will impossible to get a earth loop, as it seems there are no dc loop meters. Is there regs for DC?

 

[spark 68]

Hi Mr Enigma,

As I said, usually the AC distribution side to the various accessories is usually common to both systems, and the DC side is usually seperate electrically, feeding an inverter, or DC-AC converter.

So usually, your normal testing routine takes care of most of it.
The ELV type is not usually earthed on the DC side, it is usually floating, so no need to take EFLI readings, and usually you cannot if below 25/50V anyway.

As you say this is an unusual system and I would not like to commit myself, as I have neither the experience nor the knowledge of this type of system.

Edit: I believe some Marine type installs are/were DC based, it may be worth asking someone involved in the Marine electrical industry.

 

[Engineer54]

If this is a bulk battery bank supplied system, it's the battery charger and batteries you need to check for correct operation. A ''Big Warning'' here, these battery banks can be extremely dangerous to work on, and if you have no knowledge/experience of these systems, leave well alone, and get someone that does know his way around these battery DC systems. There is a very real chance of explosion, so ''ALL'' tools need to be of the totally insulated type, .....Mega expensive!! lol!!

 

[Guest 004]

I am just going to pull fuses, (positive and negative) do an IR, and an r1r2, no cpc, but installed in conduit, so will use that as my r1.

 

[antlewis]

My great-uncle, a former coal mine maintenance electrician (who is 76 and still working!) is the maintenance sparky on football ground near me. The ground in question has a similar system for its emergency lighting in the oldest stand (built in the late 60s). I will see if I can get some info on this for you.