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Topic Title: Type of RCD
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Created On: 25 February 2010 08:30 PM
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 25 February 2010 08:30 PM
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jcm256

Posts: 1889
Joined: 01 April 2006

I thought you went into an electrical shop or DIY store bought an RCD device or a consumer unit with a few installed and away you went, but an abstract from article I was reading (below) there may be more to it. Doesn't say really what type of RCD you should use in domestic, is it just the general type RCD and an S Type used. However they must make the other types for something, they only explain type A.

RCDs fall into three categories in terms of their response to different types of residual
currents, as follows:
i) Type AC RCDs which can detect full wave AC residual currents only.
ii) Type A RCDs which can detect full wave AC and pulsating DC residual currents.
Pulsating DC fault currents can be produced by any load incorporating
power control devices such as rectifiers, thyristors, etc.
iii) Type B RCDs which can detect full wave AC, pulsating DC and pure DC
residual currents.
(Type B RCDs are not normally used for domestic applications)
3.6 Operating Times
RCDs fall into two categories in terms of the time taken to respond to and clear residual
currents, as follows:
i) General Type These RCDs have no specified minimum response time but have
specified maximum response times as follows.
IN < 300mS
5 IN <40mS
ii) S Type These RCDs, commonly known as delayed types, have specified
minimum and maximum response times, as follows.
IN 130 - 500mS
5 IN 50 - 150mS

The following characteristics of the installation and load will need to be taken into
account when selecting an RCD:
i) Supply system, TN-C-S, TT or IT
ii) Supply voltage & frequency
iii) Maximum load current seen by the RCD
iv) Whether or not undervoltage release is required, and if it is, whether or not
reactivation of the load on restoration of the supply is required. Undervoltage
release will usually be related to the type of load on the installation.
v) Type of load, e.g. AC load only or load containing rectification or power control
Regards
jcm
 25 February 2010 09:08 PM
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daveparry1

Posts: 6239
Joined: 04 July 2007

but an abstract from article I was reading
----------------------------
An EXTRACT maybe jcm?
 25 February 2010 09:12 PM
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rikhill

Posts: 411
Joined: 18 October 2007

Come on Dave - Not only pedantic, but wrong!!

"An abstract is a brief summary of a research article, thesis, review, conference proceeding or any in-depth analysis of a particular subject or discipline, and is often used to help the reader quickly ascertain the paper's purpose"
 25 February 2010 09:18 PM
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daveparry1

Posts: 6239
Joined: 04 July 2007

Straight from Wikipedia, we live & learn rik!
 25 February 2010 09:26 PM
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rikhill

Posts: 411
Joined: 18 October 2007

Can't beat a bit of wikipedia

I might go and look up their definition of a circuit now
 25 February 2010 09:44 PM
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rikhill

Posts: 411
Joined: 18 October 2007

To go back to the OP :

The descriptions of type are fairly clear - for a long time AC would have been fine in a domestic as most loads were resistive, with increasing use of semiconductor devices (In PC power supplies for example) the resulting wave distortion could cause them problems.

Type A copes with this distortion to the waveform and would be a better choice for most installs.

I think type B are quite expensive hence the note about not normally used in domestic.
 25 February 2010 10:12 PM
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jcm256

Posts: 1889
Joined: 01 April 2006

Believe it or not I did not know that now mostly type A for Domestic.
Thanks.

I now think the rest of the question was a bit over the top, was only asking as you do not take much heed or time really in determining the characteristics of a RCD in large industrial installations unless you are designing the installation. I suppose you should do in a PIR.
Abstract could mean - to remove or extract. Not thinking clearly when writing was a bit out of sink I admit.
Thanks.
jcm
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