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View Full Version : IEE 17th Edition, RCDs, and INVERTERS



Makeit go Right
18-07-2008, 01:25 PM
I’d like to prompt some replies starting out with my understanding of this matter:

I have been trying to establish how the 17th Edition impacts on installation of Inverters, which I have previously kept away from RCDs to avoid potential neusence tripping caused by the Inverter (ie, call-backs, alterations etc etc).

I know Daikin have a general note in their installation manuals saying that RCDs should be provided to protect against shock and fire etc, but that seems to be a general aris-covering safety term, rather than for every model in the Daikin range. And when there is a neusence trip situation, they will say see your own electrician, of course.

Along the way, I came across a very useful internet video (from the manufacturer MK) that may be of interest to others, explaining some of the changes to these IEE Regs: www.mk.learninglounge.com/resources/sott17esv.html (http://www.mk.learninglounge.com/resources/sott17esv.html). (I have no connections to MK)

….and some prior text on the subject:
http://www.gadsolutions.biz/electrical/regulations/rcd-and-the-17th.html

Seems to impact very much on receessed wiring (eg, below wall surface or within partitioning etc), which must be protected by an RCD or RCBO.

I came up against this situation when wanting to connect a new circuit into an existing consumer unit for a 10kW Daikin Inverter; the sparkie stuck his chest out and started in with “Must have an RCD…17th Edition…whole system must comply… change board, problems, problems, problems.” Whew! Lots of problems and no real solutions – very unhelpful.

As far as I can see (so far), if installing a new circuit in existing board that does not have RCD protection, and the cable will be recessed into a wall/ceiling/floor (less than 50mm), it should be fed via an RCBO rather than the regular MCB. UNLESS special protection like metal conduit(earthed) is being used to protect the cable, or if run in SWA cable with the steel wire covering properly earthed.

Alternatively run it all as surface wiring so it is not in the ‘recessed’ catogory at all and thus skirt around this issue.

We will be runing an SWA power supply cable, fed via an ‘unprotected’ regular MCB in the existing consumer unit (ie unprotected meaning a circuit without an RCD), in this case because:
a) We will be running the cable surface (ie not beneath the wall surface)
b) The power cable will be an armoured cable, protected with the steel wire earthed, earthed, which would cover the ‘protected cable’ issue addressed in the 17th Edition Regs.
c) The control cable to the wall-mounted controller would be in 2 inches of surface mini-trunking.

# Anyone come up against these 17th edition issues already and resolve it elsewise?
# Any comments on the SWA cable as a way of working around the RCD issue?
# Presumably any cable run in surface trunking would avoid the issue.
# Has anyone been installing RCDs with inverters and have useful comments on this?

(Note: A similar thread has some related info, prior to 17th Edition: http://www.refrigeration-engineer.com/forums/showthread.php?t=12125)

Billy Ray
18-07-2008, 07:00 PM
That does not sound right!!

are we getting confued with fues/mcb's/rcd's etc for domestic power supplies etc.

i can understand 17th regs requiring rcd's on all circuits within a domestic dwelling, thats make sense, all round protection.... good idea..

this surely does not include for comercial installations..

are we saying an item of supply in comercial application requires an RCD?

would not of thought so..

any sparky's please bring me 'the light of hope'

Billy Ray

(fuse wire only ever used [30 Amp in all applicatrions] )

Makeit go Right
22-07-2008, 08:59 AM
"this surely does not include for comercial installations." -Billy Ray

Well, the IEE Regs apply to both domestic and commercial applications, unless it states that a particular requirement that a reg is just for Domestic or just for Commercial. As far as I can see on this, the RCD requirement applies to both, though has much more impact on the Domestic, where almost all of the cabling is hidden below the surface of a wall/ceiling etc. (The above video covers this quite well.)

MRcoolingMAGIC: your English is quite good....we tend to use Inverters most of the time in the domestic application, as they have less impact on the power and lower running costs.

frank
22-07-2008, 12:37 PM
Lets not forget here that the 17th Edition BS7671: 2008 is just a STANDARD, i.e. a 'GUIDE'.

It is not yet incorporated into law.

Being able to show that your installation/design meets the requirements of the Guide would be a good defence in a Court of Law should anything untoward happen.

Obviously, if a contract between two parties stipulates that all electrical design/installation work must comply with the Standard (BS7671:2008) then it becomes a legal document.

sinewave
22-07-2008, 06:57 PM
Being a Sparx as my first trade I feel I must contribute to this question. :)


Tis trus that the current 17th Regs apply to both commercial and domestic installs.

Within reason most electrical supplies for A/C installs in a commercial environment will be one of the following.

A) SWA to an outdoor/indoor unit

B) T/E in a suspended ceiling

C) T/E / Singles in dado trunking

D) Suface mount in conduit/trunking


All the above may be installed without 30mA RCD protection using just an MCB with a compliant Zs at the point of utilisation.

If it's a small commercial unit or domestic premises that is having, or has had a radial circuit buried in the fabric of a building at a depth of less than 50mm without an earthed protective sheath/capping or conduit then it's a 30mA RCD or RCBO


Clear? :)


As mud! :p



As an aside to this I've put quite a few small splits in on RCD circuits out of neccesity and had no problems, so I feel this scaremongering amongst some manufactures is un called for.


Bigger systems maybe, but in most cases worry yee not! :cool:

Makeit go Right
22-07-2008, 09:35 PM
I found some helpful info from the ECA website: "KEY FACT SHEET on The 17th Edition and RCDs."

It defines "under the supervision of a skilled or instructed person" and several exemptions, all of which is useful to aircon installs.

http://www.eca.co.uk/IndustryGuidance/Technical/17th%20edition/17_edition_factsheet_02.pdf

sinewave
22-07-2008, 09:50 PM
Good link MIGR!

christhespark
21-08-2008, 01:57 PM
I’d like to prompt some replies starting out with my understanding of this matter:

I have been trying to establish how the 17th Edition impacts on installation of Inverters, which I have previously kept away from RCDs to avoid potential neusence tripping caused by the Inverter (ie, call-backs, alterations etc etc).

I know Daikin have a general note in their installation manuals saying that RCDs should be provided to protect against shock and fire etc, but that seems to be a general aris-covering safety term, rather than for every model in the Daikin range. And when there is a neusence trip situation, they will say see your own electrician, of course.

Along the way, I came across a very useful internet video (from the manufacturer MK) that may be of interest to others, explaining some of the changes to these IEE Regs: (I have no connections to MK)

….and some prior text on the subject:
Seems to impact very much on receessed wiring (eg, below wall surface or within partitioning etc), which must be protected by an RCD or RCBO.

I came up against this situation when wanting to connect a new circuit into an existing consumer unit for a 10kW Daikin Inverter; the sparkie stuck his chest out and started in with “Must have an RCD…17th Edition…whole system must comply… change board, problems, problems, problems.” Whew! Lots of problems and no real solutions – very unhelpful.

As far as I can see (so far), if installing a new circuit in existing board that does not have RCD protection, and the cable will be recessed into a wall/ceiling/floor (less than 50mm), it should be fed via an RCBO rather than the regular MCB. UNLESS special protection like metal conduit(earthed) is being used to protect the cable, or if run in SWA cable with the steel wire covering properly earthed.

Alternatively run it all as surface wiring so it is not in the ‘recessed’ catogory at all and thus skirt around this issue.

We will be runing an SWA power supply cable, fed via an ‘unprotected’ regular MCB in the existing consumer unit (ie unprotected meaning a circuit without an RCD), in this case because:
a) We will be running the cable surface (ie not beneath the wall surface)
b) The power cable will be an armoured cable, protected with the steel wire earthed, earthed, which would cover the ‘protected cable’ issue addressed in the 17th Edition Regs.
c) The control cable to the wall-mounted controller would be in 2 inches of surface mini-trunking.

# Anyone come up against these 17th edition issues already and resolve it elsewise?
# Any comments on the SWA cable as a way of working around the RCD issue?
# Presumably any cable run in surface trunking would avoid the issue.
# Has anyone been installing RCDs with inverters and have useful comments on this?

(Note: A similar thread has some related info, prior to 17th Edition:

If the circuit run entirely on the surface, you do not need to use an RCD.
Likewise, if it is buried to a depth of less than 50mm, a cable encorporating an earthed metallic sheath, such as steel wire armoured armoured cable can be used. (Other lighter weight cables are due out soon!)NB, We have also protected cables only where buried over a short length IE to the drop down to a controller, and covered the chase with an earthed 3 inch strip of 2mm galv steel.
Hope this helps.
Chris

pactor
22-08-2008, 09:15 PM
I have passed the 17th ed but I am in Ireland and don't have the book to hand, I will be back sunday, but there are exceptions. I sure one is where the installation is under the control of competent persons.

christhespark
27-08-2008, 12:04 PM
I think that what is meant by "installation is under the control of competent persons". is restricted to areas under lock and key with no public access, such as lift motor rooms, plant rooms, sub stations and the like.
Niceic technical will give guidance - even if not a member.