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Why cant you cross a 12v cable with a 230v cable (Read 7027 times)
daiglo
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Why cant you cross a 12v cable with a 230v cable
Jul 22nd, 2008, 8:06pm
 
Trying to wire in 8x  50w 12v spots but reading the transformer instructions it advised you cant cross a 12v cable with a 230v cable.  My existing cables would be 6 inches below why will this cause an issue?  I have made sure the transformer has the correct loading and the cables are the correct size and distance but I can’t see why this is an issue with crossing the wires?  Help me out   Embarrassed
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cosbycarl
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Re: Why cant you cross a 12v cable with a 230v cab
Reply #1 - Jul 22nd, 2008, 10:03pm
 
Assuming i have read what you have written properly, you have to separate 12v low voltage from 230v mains voltage because of interference caused from the 230v to the 12v cable? Hope this helps, its a regulation.
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londonman
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Re: Why cant you cross a 12v cable with a 230v cab
Reply #2 - Jul 22nd, 2008, 11:09pm
 
Quote:
Assuming i have read what you have written properly, you have to separate 12v low voltage from 230v mains voltage because of interference caused from the 230v to the 12v cable? Hope this helps, its a regulation.



Which one? Just curious...always like to go back to the source. I can't quite see what impact any mains borne interference is going to have on my halogen bulb so I'd like to learn why.
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sparky415
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Re: Why cant you cross a 12v cable with a 230v cab
Reply #3 - Jul 23rd, 2008, 6:43am
 
Daiglo,

If you are only talking about a couple of foot of cable its not going to make a bit of difference
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Lectrician
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Re: Why cant you cross a 12v cable with a 230v cab
Reply #4 - Jul 23rd, 2008, 6:59am
 
The cables can cross over each other, but not run parallel to.

I know the instruction manuals often show a picture of the two crossing with a huge cross through it.  This is to cover them - they go OTT.

It is to prevent 240v being induced into the 12v supply, which is not going to happen if you cross at 90°.  It also prevents the high frequency noise of the 12v (it is not 50hz - it is very high frequency) from entering the mains distribution and causing noise on your stereo or TV for example.  This is what the tranny manufacturers are trying to prevent by getting you to keep them completely clear - They don't like phone calls saying "When I turn your lights on, my stereo humms".
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cosbycarl
Re: Why cant you cross a 12v cable with a 230v cab
Reply #5 - Jul 23rd, 2008, 5:22pm
 
AAAAhhhh, well there you go, neva knew that but do now.

To londonman, you do have to segregate LV from 230v, i dont know the reg number or even what section, haha, ive not looked, but like lec said that applies to cables run in parallel with each other i.e in trunking runs, the trunk has to be segregated.

Lec, does that apply to sky cables too? If you crossed a 230v supply cable (armour) across them?

Cheers
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sparky415
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Re: Why cant you cross a 12v cable with a 230v cab
Reply #6 - Jul 23rd, 2008, 5:42pm
 
Carl,
It applies to all cables that run in parallel (along side/next) to each other but cables can cross each other with out inducing a voltage
(But in this case its not worth worrying about)

In theory a properly earthed armored cable shouldn’t affect LV cables but its better to avoid running them too close but as you are crossing them it should be ok

If I remember rightly you can (Im sure someone will tell me if Im wrong) run LV cables with 230v if they are insulated to 230v standard Ie; you can wire a doorbell in 1.5T&E but you might find the bell ringing every time the washing machine on  Smiley
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cosbycarl
Re: Why cant you cross a 12v cable with a 230v cab
Reply #7 - Jul 23rd, 2008, 6:12pm
 
Cool,

The plummer put his water feed up a wall and thru the "bracket" of a sky dish, i was gonna run it along with the water feed to supply a container for work, the plummer had the idea of running the water feed along the roofs of the long line of terraced bungalows, so i was gonna cable tie all the way along with his water pipe, but instead we used catinary to go from the outside of the boiler room which was where the cu was, all the way to a scaffold, of which was actually rigged for me to put the supply in which i was unaware of at the time (lack of communication), then from the scaffold to the containers, it was about a 40-50 meter run, perfect weather for it today tho!!

Also what i wanted to know, it in regards to testing which i dont normally have a problem with, when i finished the job, i took a Ze at the containers cu and i did an IR test as well as R1+R2 which was good, I then did a Ze at the boiler house CU and tested the RCBO and then i tested the cu which was the communal one which supplied various circuits as well as the boiler room and done a Ze and kA there, now, I only have DIEC's, i know you gotta test each distribution circuit as well as the newly installed final circuit, but where do i put all the Ze figures when all ive got is one place for Ze single phase and one place for Ze three phase. Ive not been given any continuation sheets and i know these Ze results need to be recorded, so through no options i put down the readings of the main cu in the mains room, and i know thats not correct!
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Re: Why cant you cross a 12v cable with a 230v cab
Reply #8 - Jul 25th, 2008, 7:09am
 
You should not be using a domestic cert on a commercial site for a start!

You use continuation sheets for each submain.

I suppose you could record the true Ze at the origin as usual, and then use a line each for the submains.  The 'ze' measured at the submain boards is not a Ze - It's a Zs, but to cause less confusion, is called a Zdb.
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cosbycarl
Re: Why cant you cross a 12v cable with a 230v cab
Reply #9 - Jul 25th, 2008, 9:57pm
 
OOOooohh touchy lec,

I can only use what im supplied with, if thats work gives me what else am i supposed to do when they say test it? I can say no but they will just get somebody else to do it! i didnt think of it as being commercial to be honest considering the supply came from a flat, and ok on the continuation sheets and cheers for letting me know its Zs and not Ze, i do know the difference tho, but didnt know about Zdb

thanx
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