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Topic Title: Caravan park. Permanent site.
Topic Summary: Ze 1.58 0hms.
Created On: 16 June 2013 11:15 AM
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 16 June 2013 11:15 AM
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microy

Posts: 352
Joined: 25 October 2005

According to The Electricians Guide to the 17th, by John Whitfield, regarding the Ze at the hook-up point. "It is recommended that the the earth fault loop impedance at the plug should not exceed 2 Ohms"
The hook-up and the caravan are both protected by 30mA RCDs.
I am getting 1.58 Ohms so it appears to comply but this obviously affects the Zs readings inside the caravan and thereby the disconnection times.
All reading in the caravan are ok except high zs on all circuits.
Advice saught on coding.
Mike
 16 June 2013 11:23 AM
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dickllewellyn

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What readings are you getting? And what readings are you expecting?

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Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 16 June 2013 11:41 AM
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microy

Posts: 352
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In the caravan I get Ze 1.58.
Sockets. Zs. 1.85.
Lights Zs. 2.04.

Mike
 16 June 2013 12:29 PM
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slittle

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What's the earthing type ??

That should give you a good clue

Stu
 16 June 2013 12:43 PM
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microy

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Stu.
TNS.
If it was TT it would be a good reading.
It's the 2 Ohms of Whitfield (Page 197) that's throwing me.
Mike
 16 June 2013 02:05 PM
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daveparry1

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If it's all 30m/a rcd protected you could in theory have a Zs of 1666 ohms! If the book says <2 ohms and you're getting 1.58 ohms what are you worrying about?

Dave.
 16 June 2013 03:23 PM
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slittle

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Thought it was a bit good (but not impossible) for TT :-)

I've just had a quick canter through section 708 and can find no reference to the 2 ohms. It does say imply that even for TNS supplies the pitch points should have their own electrode but otherwise nothing exciting.


Stu
 16 June 2013 03:55 PM
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microy

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Stu.
I also searched the good book without any joy. That's why I checked with Whitfield.
My problem was with the max measured efli of 1.15 for the 32Amp MCB,
Mike
 16 June 2013 05:43 PM
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perspicacious

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What is the maximum prospective fault current at the pitch socket-outlet?

Regards

BOD
 16 June 2013 05:50 PM
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maltrefor

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My problem was with the max measured efli of 1.15 for the 32Amp MCB


Down rate to a 20Amp RFC or split it into 2 radial cct's instead.
 16 June 2013 06:36 PM
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microy

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Bod.
The maximum pfc at the hook-up is 138.6Amps.
Mike.
 16 June 2013 06:42 PM
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microy

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Maltrefor.
I appreciate the advice but at the moment I'm just seeking advice on the coding for the EICR.
Mike
 16 June 2013 06:53 PM
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perspicacious

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"The maximum pfc at the hook-up is 138.6Amps"

Is that to earth or neutral Mike?

Regards

BOD
 16 June 2013 08:34 PM
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jcm256

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microy

What is the problem that is bothering you if If the system Ze value is too high to achieve rapid enough disconnection with the overcurrent protective devices available then it is necessary to use one of the two following methods:
1, fit a cable with a larger cross-section and consequently a lower
impedance. Or
2. use a residual current device (RCD). Subject to certain
Conditions being met this provides a simple and economical
solution

For caravans you must use an RCD for shock protection anyhow, therefore every circuit in the caravan lights, sockets, heating will be protected as long as you have an effective earth.

. Section 708, 'caravan and camping parks' (formerly 'caravans, motor caravans and caravan parks') is now divided into section 708 and section 721, 'caravans and motor caravans'. Of particular note is that each pitch socket outlet is to have separate 30 mA RCD protection + pitch supply 100mA separated from any other supply. See: 2011 40 Autumn Wiring Matters - IET Electrical


I think I know what you are on about in the event of a
defective RCDa or a sluggish overcurrent
protection device such that the faulty circuit
might remain in an energised state for quite
some time, and a person in the caravan would
be exposed to a touch voltage. (Unlikely like winning the lottery to happen)


In General the RCD will not operate on overcurrent, or short circuit but you will have OCPD such as a fuse or circuit breaker and used with an RCCB, or be incorporated into the RCD as in an RCBO. It is important to ensure that where an external OCPD is used, the rated load
current of the RCD is not less than that of the OCPD, otherwise the RCD may be damaged during overcurrent conditions.

Something is missing to get the 2 ohms bother out of your mind, would like to know what it is for a further solution to the problem.

Regards
jcm
 16 June 2013 09:26 PM
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microy

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Thanks for the replies. I will give it a code 3.
Mike.
 16 June 2013 09:37 PM
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perspicacious

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Just wondering how the EICR on the site wiring reads with regard to the 32 A pitch outlet on a TN-S system with Zs at 1.58 Ohms (411.4.7) and 525.101.

Regards

BOD
 16 June 2013 10:00 PM
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sparkingchip

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Why does the pitch have a 32 amp socket?
 16 June 2013 11:28 PM
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microy

Posts: 352
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The caravan is hard wired into the hook-up box from a 32A MCB and 40A 30mA RCD.
This is fed from a 63A MCB which is feeding 4 pitches. I have been unable to access the origin as yet.
According to the site electrician it is a TNS system and according to Whitfield a zdb of 2 Ohms is allowed at the hook-up. This 2 Ohms is a new one on me, (And apparently to the rest of the forum), Hence the post.
I have been unable to view previous PIRs, everyone on site is being is being very evasive. (I wonder why?).
I will sort it tomorrow one way or the other.
Mike.
 17 June 2013 08:51 AM
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Parsley

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Whitfield might have based the 2 ohms on the assumption that a 16A protective device was being used.

What was the L-N loop impedance at the hook up point?

Regards
 17 June 2013 09:16 AM
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dickllewellyn

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Is this touring caravans, or is it park homes/static caravans?

-------------------------
Regards
Richard (Dick)

"Insert words of wisdom and/or witty pun here"
IET » Wiring and the regulations » Caravan park. Permanent site.

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