IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Just in the morning.
Topic Summary: Old wiring
Created On: 04 August 2012 02:01 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.
 04 August 2012 02:01 PM
User is offline View Users Profile Print this message



sowie1959

Posts: 42
Joined: 18 December 2006

Just a quick question. I have a fault on a lighting circuit which was added to about 5 years ago. The fault only appears when the lights are switched on first thing in the morning, causing the mcb to operate. When the mcb is reset everything is fine. The building is an 1930`s wood building with stranded cable installation.
 04 August 2012 02:04 PM
User is offline View Users Profile Print this message



DOUGIE1000

Posts: 4148
Joined: 13 August 2005

Surely you have done IR test? For a start?

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 04 August 2012 02:09 PM
User is offline View Users Profile Print this message



sowie1959

Posts: 42
Joined: 18 December 2006

An IR test gives me 0.02 rising to clear and then when retested all clear.
 04 August 2012 02:50 PM
User is offline View Users Profile Print this message



DOUGIE1000

Posts: 4148
Joined: 13 August 2005

Look for water/damp ingress.

Edited to add -

Chech ceiling extract or fan or online fans for water through ducting.

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 05 August 2012 11:21 AM
User is offline View Users Profile Print this message



jumpinjax

Posts: 54
Joined: 13 December 2008

This is obviously a commercial premises as the lights are switched on in the morning, if they are fluorescents then I would start checking for a faulty ballast or even an overloaded mcb or wrong type(b instead of a c) if of course obvious water ingress is not a problem as mentioned
 05 August 2012 12:50 PM
User is offline View Users Profile Print this message



alancapon

Posts: 5745
Joined: 27 December 2005

Originally posted by: sowie1959
An IR test gives me 0.02 rising to clear and then when retested all clear.

This is likely to be your test meter charging suppression or power factor correction capacitors in the circuit. It is likely that your meter leaves the circuit charged at the test voltage after the test is finished. A new test reads infinity, as the capacitors are still charged.

Regards,

Alan.
 05 August 2012 07:51 PM
User is offline View Users Profile Print this message


Avatar for davezawadi.
davezawadi

Posts: 2615
Joined: 26 June 2002

Interesting questions come to mind.
1) Is this a new phenomenon, or has this always happened? Fittings with PFC capacitors often need circuits with type C or even D breakers to prevent the charge current tripping them. If new then something has changed, probably the capacitors have been replaced?
2) If this doesn't happen every time the circuit is energised, why not? Has the MCB been replaced or anything else?
3) It is likely that there is a fault present which clears after powering up, and reappears after a period. This may be polyester (self healing) PFC capacitors, just disconnect each PFC cap in turn, and the fault will go away.

-------------------------
David
CEng etc, don't ask, its a result not a question!
 08 August 2012 05:47 PM
User is offline View Users Profile Print this message



sowie1959

Posts: 42
Joined: 18 December 2006

Give the last man a medal. The was a small spike to earth. This was after a period of time turned off. Also should of mentioned this is a pre- war wooden hut that has had little or no maintenance since being built. I later found out this had been a problem since the install of the new lighting.
Thanks for all the help.
Statistics

See Also:



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