Metrel Reading

[sparkie_Al]

Hi
Doing Zs on a stage lighting rack system, my metrel easitest faithful.....gave me a reading of >20 ohms (sign) and underneath rLn. I know that there are electronics involved with the rack system, and I am half tempted to test the unit with the PAT tester, seperately.
I was checking each circuit to the stage lights, as they are plug in 15amp sockets independant of each other, and if I plug these circuits into the bottom row of sockets (rack-a) the tester tests correctly. If I plug the same circuits into the top rack (rack-b)(separately powered from a)the tester will not test,and produces the result above. cannot understand result as >20ohms....so what, test an earth rod and you can get 300+ ohms. if L/N were reversed then you get a flashing L-N. rLn =? resistance between L/N...? If you plug the lights into top rack, they all work correctly, so I do not want to fail anything here, as it just may fall out of the criteria for the testing method.

 

[Rockingit]

Hi Al, why are you trying to Ze lighting bars?? There's no need, basically.

you'll be lucky to get anything useful through a theatre lighting rack. Most of them are internally wired as 3ph with 1ph mods, the socket outlets will be wired (on most makes) straight out of the triacs via a breaker or 10A fuse and there's so much suppresion ironmongery it's just a lost cause. The best you're likely to do will be to IR and L1L2 the individual circuits back to the bars (and watch for common cpc's and dodgy bonding practice on the IWB's) and then Ze the incoming supplies (on 63A's?).

Ze values for theatre lights is just a pointless cause really, as 1) it's specialist equipment; 2) the lamps don't care about a disconnection time, they're on a protected dimmer anyway; 3) any reading you might get is likely to be wrong anyway and 4) both the bars, lights and dimmer assignments are regularly repatched, so any value that you might achieve on a test sheet is destroyed the next show that comes in.

Hope that helps, ask away if not!

 

[sparkie_Al]

Hi Thanks for reply
Doing circuit impedance. Was really just testing everything was safe. The circuits are wired in singles, fixed in plastic conduit, to 15amp socket outlets, so thought I could plug the individual numbered circuits in, and Zs them the same way you would for say a ring main/radial.
This lighting rack does not include dimmers that I can see, although the circuitry would undoubtably contain triacs. The fusebaord is 100amp with two 32amp mcbs for the two BS4343 (whatever they are now)sockets, One per rack. Would like to know what the reading meant from the tester, as I have not seen that come up before, and also it is not in the book of words that came with the tester.
I had been asked to check the Stage lighting, which is based in a school, and had not been used for a long time.
Interestingly I could not find any standard that the lighting had to meet, especially within BS7671, and the last "certificate" was literally a plain piece of headed notepaper stating that the system was safe to use....that was it!(1993 BTW)
Lighting Racks are Switchmaster 600. Google that and you just get Drayton heating controls.....

 

[Rockingit]

You will find if you turn the racks around that there are either 6pin or 8pin DIN sockets on the back, working at +10v DC, these link back to an analogue lighting control desk (if it's a school then probably Pulsar). They are dimmer racks, just may not look like something you've seen before. The biggest risk with school lighting kit is wear and tear on the lanterns; glands, dodgy lamp housings and bad earthing. Obviously, as it's all wired in 15A it's unfused but the dimmers aren't RCD protected so if you get an earth fault then it's all hell let loose. Extension cables also and adaptors. I don't recognise 'Switchmaster' either, but then if they're either very old (or very new) then they could be a copy of any Strand variant. My guess is that they will be 6 x 10A outlets each (this was standard) but most schools either didn't have the budget or some pseudo safety reason so the incomers were downed from 60A to 30A - often presented on 32/63A ceeform - which actually makes them more prone to overload, of course, as it's the OUTputs not the inputs where the fuse/breaker is.

Can't help with the Metrel display message, mine hasn't ever shown me that either!

 

[sparkie_Al]

Hi
the local stage fuseboard has at least RCD protection, and worked correctly from the bottom rack doing circuit rcd auto testing.
There are also audio outputs in this sytem, with various din sockets around the stage area and the hall too. When I was aked to check the system I was told there was "sound to light" facility within the system.

I was impressed with the metrel, and took a photo of the output display, dont know how to upload that though.
Thanks for the help.

 

[DaveyD]

took a photo of the output display, dont know how to upload that though

Click on insert image (the tree) and browse for file on you PC to upload.

 

[Rockingit]

OK, getting slightly more complicated now; any jack sockets will be (well, would normally be!) INputs from audio, but I wouldn't expect to see them on the racks, I'd expect to find them on the desk or another dedicated controller. The DIN sockets spread around the venue would normally be so that the desk/s can be moved around to suit the show and patched back accordingly. Theatre kit has always had a modular approach. The sound to light bit doesn't affect you for testing (as it'll be ELV), nor too does the lighting control system as again it's all low voltage DC no matter which version it is.

It's good that the racks have had RCD protection provided upstream, not sure why one would behave differently to the other but personally I wouldn't have tried to ramp test through them, you stand a reasonable chance of damaging the triacs.

If you get a bit stuck at any point (not suggesting that you are!) I've a couple of theatre spark old mates in the Cheltenham area I can put you in touch with.

 

[sparkie_Al]

Ah, ok will give that a shot later on.

 

[MarkieSparkie]

Hi
Doing Zs on a stage lighting rack system, my metrel easitest faithful.....gave me a reading of >20 ohms (sign) and underneath rLn. I know that there are electronics involved with the rack system, and I am half tempted to test the unit with the PAT tester, seperately.
I was checking each circuit to the stage lights, as they are plug in 15amp sockets independant of each other, and if I plug these circuits into the bottom row of sockets (rack-a) the tester tests correctly. If I plug the same circuits into the top rack (rack-b)(separately powered from a)the tester will not test,and produces the result above. cannot understand result as >20ohms....so what, test an earth rod and you can get 300+ ohms. if L/N were reversed then you get a flashing L-N. rLn =? resistance between L/N...? If you plug the lights into top rack, they all work correctly, so I do not want to fail anything here, as it just may fall out of the criteria for the testing method.

The rLn error message is telling you that your measurement has exceeded the preset continuity high limit (which is set via the setup menu) of 20 Ohms in this case.

 

[sparkie_Al]

Hi
It may well be past a preset limit, but I was doing earth loop not continuity. Preset is the thing though as there is no adjustable setupo menu as such.

Doing earth loop I would not expect to damage the triac...get a strange result, maybe, but then also I assume when you say "Ramp" past , you mean just that and not performing the rcd ramp-test.


The cables that go off to the din sockets around the area, do seem to be connected within these racks. I will have to go back and take a photo of that also.

 

[sparkie_Al]

Just thought---BTW, that I tried using "trip lock" as well, which would give you a higher preset. The Robin, does 20/20000, that tested it at first, with a result of 105ohms, but the next time it lit up an LED and would not test.

Sorry just a thought.

thanks for the interest.

 

[sparkie_Al]

MarkieSparkie is absolutely right (before you jump on me) Zs is tested in Ohms, and it would be a preset. The trip lock is tested upto the setting of the rcd, and if you study the shot the tester is on trip-lock. sorry being a numpty there.....long day.

 

[Rockingit]

Al, either which way the meters work or don't, you shouldn't be trying to get a Zs through the dimmer racks 1) it's pointless and 2) they are electronic devices. It would be a bit like connecting your croc clips to the toaster elements! BS4533 is the relevant document here (and parts of 7909).

 

[sparkie_Al]

Ok Point taken, will look up the BS, so thank you for pointing that out.

In general then the headed notepaper from the last contractor, just stating it was safe to use, is all that was required?, no testing of light-fittings, etc....off to research, thanks for help.
Al

 

[Rockingit]

You're testing the INSTALLATION, not the equipment. So that is why there is no point in worrying about Zs on final circuits, because the circuits are designed to be powered from specialist equipment - think about it; the disconnection time is dependant on the electronics and fuses in the rack, not the loop between the bulb and the incomer in the basement.

So, the testing I would do is:

Visual inspection then;
R1R2 (Rn) on each circuit
IR on each circuit

Bonding to the bars etc

R1R2, IR, Zs & RCD etc (as appropriate) from the rack SUPPLIES back to the feeding DB

PAT test the Racks as class 1.

Final testing: is the beer any good down the road. Job done.