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Topic Title: External car charger
Topic Summary: TT Earthing
Created On: 01 May 2013 07:59 PM
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 01 May 2013 07:59 PM
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circle143

Posts: 220
Joined: 19 July 2007

Hello

I am installing an outdoor dual outlet single phase charger - which will be supplied by two separate circuits wired in SWA -which will be TT at the charger.

I have two methods for this - come from the DB with appropriately rated mcb's to an external isolator and then fit rccb's inside the charging unit.

or

The DB is a crabtree polestar - could I use appropriately rated rcbo's (as these need no earth connection) in the DB and then go to the isolator and into the charging unit - bearing in mind this will be TT

The job and the spec has altered several times and I might not being seeing it clearly.

Advice welcome, thanks
 01 May 2013 08:48 PM
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dickllewellyn

Posts: 1222
Joined: 19 March 2010

I believe the IET have published a code of practice for EV charging points, it might be worth you having a read.

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

"Insert words of wisdom and/or witty pun here"
 01 May 2013 08:58 PM
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dbullard

Posts: 1166
Joined: 02 March 2006

Yes TT it, you can RCBO it at the supply end if required.

The IET guidance note is a great guide if you require any advice PM me and I will only be to glad to help, what type of charger are you going to use, and what make of car as many use the same type of plug, but some require a manufacturer supplied lead, believe it or not some charge extra for the lead !!!!!

Regards

Daren

-------------------------
..... Dont pee in my pocket and tell me its raining ......


www.quest-electrical-sw.co.uk
 02 May 2013 11:21 AM
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AJJewsbury

Posts: 11768
Joined: 13 August 2003

Two possible problems come to mind - due to BS 7671 requirements that:
Metalwork connected to two different earthing systems can't be in reach of each other (411.3.1.1), and all the exposed-conductive-parts protected by same device need to be connected to the same earthing system (411.5.1).

I suspect those will be difficult to achieve if the SWA is glanded to a metal clad DB containing the RCBOs - although not impossible - SWA gland insulated from DB but connected to the TT earth, internal wiring double-insulated and the gland/armour outside the DB covered so they can't be touched simultaneously with the DB or other TN earthed equipment.

Probably easier to use MCBs in the DB, have the armour connected to the TN earth, and gap it at the charger end and have the TT RCD it there - like a typical TT garage setup.

- Andy.
 02 May 2013 02:34 PM
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Parsley

Posts: 1090
Joined: 04 November 2004

The type of RCD needs to be considered, type B may be needed.

Regards
 03 May 2013 04:40 PM
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circle143

Posts: 220
Joined: 19 July 2007

Thank you for the replies - its appreciated
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