IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Does it matter if I connect the supply to the bottom of an RCD?
Topic Summary:
Created On: 13 August 2014 09:45 PM
Status: Post and Reply
Linear : Threading : Single : Branch
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 13 August 2014 09:45 PM
User is offline View Users Profile Print this message



QuietOne

Posts: 43
Joined: 28 February 2014

Good evening.

I was hoping find out if an RCD can be connected up with the supply at the bottom or the top of the device? After looking through the internet it seems a bit inconclusive but the majority of answers seem to be 'yes'.

I would also appreciate it if someone could explain the wiring diagram on the left face of the RCD to me as I expect this gives the answer, below is a link to the exact same RCD that I have (80A BG RCD):

http://www.builderdepot.co.uk/...le-2-module-30ma.html
Text

Many thanks
 13 August 2014 11:00 PM
User is offline View Users Profile Print this message


Avatar for stateit.
stateit

Posts: 2227
Joined: 15 April 2005

WRT the diagram:

Blimey, no-one's explained it yet: I'll give it a shot, but I've no MEng or PhD...

N & L have a coil around them attached to sensing mechanism (calibated to nmA). This is linked to a contactor which is connected to a spring which will throw the DP contacts open.

Couldn't tell you if the contactor is NO or NC. Someone will.

When there is no current imbalance the sensing mechanism/ contactor remain in their happy state (my own technical term)

The test button is tapped to N & L. When pressed it closes the circuit , which will throw the contactor, opening the DP switch.

I hope some one else will pitch in with a more accurate explanation...

[edit] And the RCD will operate if incoming is connected top or bottom, though my understanding is: Best practice with all switches is that the moveable contact connects to the energized contact. In your diagram, that would mean incoming Line is connected to the top. [/edit]

-------------------------
S George
http://www.sg-electrical.com
 13 August 2014 11:10 PM
User is offline View Users Profile Print this message



QuietOne

Posts: 43
Joined: 28 February 2014

Thanks Stateit,

I'm pretty happy with the way an RCD works it's more the diagram itself that I'd like to understand.

I hope that doesn't sound ungrateful as it's good of you to reply at 11pm

ps.. now I have to edit as you have edited . Thanks for the extra bit, so does that mean this one could or couldn't have the supply connected at the bottom?
 13 August 2014 11:23 PM
User is offline View Users Profile Print this message


Avatar for stateit.
stateit

Posts: 2227
Joined: 15 April 2005

And there was me thinking the explanation illustrated the diagram....

-------------------------
S George
http://www.sg-electrical.com
 14 August 2014 12:28 AM
User is offline View Users Profile Print this message



QuietOne

Posts: 43
Joined: 28 February 2014

I'm sure it did Stateit, to someone with more intelligence than myself.

I would like to know what each part of the diagram means, what the different shapes mean? However I really don't expect a reply at this time of night
 14 August 2014 09:56 AM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11768
Joined: 13 August 2003

As a first (second now?) approximation - you've a triple pole switch at the top. The rightmost two poles switch L & N. The leftmost pole is in series with the test button on the left (marked T) and below that the rectangle represents a resistor (presumably around 7.66kOhms so that 30mA by-passes the N side of the coil during a test). The oval toward the bottom represents the torroid with the main L & N passing through it. The rectangle to the right is the electronics that detect the level of leakage and decide whether to trip or not (and for an S type implements the time delay) and the bit above that is the actuator that operates the 3-pole switch we started with (akin to a contactor coil if you like, but probably energised to trip rather than hold-on).

In principle it doesn't matter which way around an RCD is wired (top or bottom) but some subtle details in some models can make a difference - e.g. if the test button is wired to PE rather than supply N, or a earth-missing detection circuit - more common on RCBOs rather than RCCDs of course. And which side the electronics are supplies from might make a difference during insulation tests etc.

Swapping N-L can be dodgy though as some models will close N first and open N last - not something you'd want to reverse.

- Andy.
 14 August 2014 11:45 AM
User is offline View Users Profile Print this message



QuietOne

Posts: 43
Joined: 28 February 2014

Thankyou so much Andy,

I have copied all of that down and it is stored next to the diagram for future reference.

Thanks again for taking the time to look at the diagram and give such a helpful answer.
 14 August 2014 01:37 PM
User is offline View Users Profile Print this message


Avatar for sparkingchip.
sparkingchip

Posts: 6335
Joined: 18 January 2003

Some manufacturers instruction leaflets used to state quite clearly that their RCDs can be connected in either direction and I have done so on many occasions.

I have a BG RCD exactly the same as you one you have posted the link to in my hand and upon opening the sealed box I have found it it has been supplied without any instructions of guidance at all, there is only the RCD in the box.

Personally I'd have no issue with connecting the RCD in either direction, but you may want to ask the manufacturers.

Andy
 16 August 2014 08:44 PM
User is offline View Users Profile Print this message



antric2

Posts: 1087
Joined: 20 October 2006

Evening,
As mentioned already, it may be an idea to seeek advice from manufacturerer but as far as i am concearned, a coil will conduct either way so RCD can be top or bottom connection to supply although it is usually 99% of the time connected as supply to the top terminals.

Recentley though, it had me wondering the same as I fitted a Schneider con unit and their RCD's are supplied from the bottom terminals.
Regards
Antric
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.