Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Helpful Answer
  • Locked Locked
  • Replies 6 replies
  • Subscribers 13 subscribers
  • Views 1576 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

How could I measure DC leakage current of a particular piece of equipment?

Paul Brewerton

I need to ensure we have the correct type of RCD, protecting the weird and wonderful equipment in our labs.

Is their a way to measure exactly how much DC leakage a piece of equipment will leak whilst in operation.

Some of the laboratories have single phase consumer units with an RCD main switch supplying multiple radials out to socket outlets, into which various pieces of kit are plugged in. 

My concern is, that without knowing how much DC the equipment is leaking, how can I determine if the correct RCD has been installed.

Ideally, I would have the Main Switch changed to a regular type and the MCBs changed for RCBOs, but before that happens, I just need to satisfy myself that the RCD installed is actually performing its function.

Thanks you for any help in advance. 

Parents
  • 0

    Thanks for the viewpoints gents. What I'm trying to do is satisfy the requirement below from the wiring matters article.

    Which RCD Type? - Electrical (theiet.org) 

    What if I discover a Type AC RCD whilst carrying out an electrical inspection during an electrical installation condition report? If the inspector is concerned that residual DC current may affect the operation of Type AC RCDs, the client must be informed. The client should be informed of the potential dangers which may arise and an assessment of the amount of residual DC fault current should be made to determine if the RCD is suitable for continued use. Depending on the amount of residual DC fault current, an RCD which is blinded by residual DC fault current is likely not to operate which could be as dangerous as not having an RCD installed in the first place.

    What I am wondering is HOW I can quantify the amount of DC leakage current that is potentially affecting the installed RCDs.

    Maybe that is too complicated and Mike you have given me an option, that would be to run everything at full power, and then perform an RCD test to see if it operates. However in this scenario we have multiple socket outlets so we do not know exacylt how much equipment is going to be plugged in and used at any one time.

    If I could check each piece of kit, quantify the DC leakage, and label, we could then control how much is affecting the RCD.

    The RCDs we have on the consumer units are Type AC, and some Type A, which will only be good for 6mA. 

    Maybe I will need to recommend upgrading to Type F, or even Type B.

Reply
  • 0

    Thanks for the viewpoints gents. What I'm trying to do is satisfy the requirement below from the wiring matters article.

    Which RCD Type? - Electrical (theiet.org) 

    What if I discover a Type AC RCD whilst carrying out an electrical inspection during an electrical installation condition report? If the inspector is concerned that residual DC current may affect the operation of Type AC RCDs, the client must be informed. The client should be informed of the potential dangers which may arise and an assessment of the amount of residual DC fault current should be made to determine if the RCD is suitable for continued use. Depending on the amount of residual DC fault current, an RCD which is blinded by residual DC fault current is likely not to operate which could be as dangerous as not having an RCD installed in the first place.

    What I am wondering is HOW I can quantify the amount of DC leakage current that is potentially affecting the installed RCDs.

    Maybe that is too complicated and Mike you have given me an option, that would be to run everything at full power, and then perform an RCD test to see if it operates. However in this scenario we have multiple socket outlets so we do not know exacylt how much equipment is going to be plugged in and used at any one time.

    If I could check each piece of kit, quantify the DC leakage, and label, we could then control how much is affecting the RCD.

    The RCDs we have on the consumer units are Type AC, and some Type A, which will only be good for 6mA. 

    Maybe I will need to recommend upgrading to Type F, or even Type B.

Children
  • 0 in reply to Paul Brewerton

    I think the wiring matters article is perhaps a bit alarmist.  It is just about credible that there may be the pulsed AC sort of fault where a device which rectifies the mains directly (switch mode supply based thing, thyristor based speed controller/ lamp dimmer maybe) develops a fault that in effect puts a diode and a resistor between live and earth. If the resistance is high enough that the dide id not blown out, then the likely rise in cpc voltage should be small.
    Personal experience suggests that commonly when the over stressed diode fails soon after,  it blows to a short condition, so creating an AC fault that then trips the RCD anyway
    A smooth DC fault is quite unlikely except in very odd cases - car chargers that run DC pilot signals over the CPC are an exception.
    Most RCDs are not blinded by 6mA anyway, it is just a very safe limit to assume in the absence of better maker's data.

    In this case is such a fault likely to persist undetected for any length of time ? If yes something should be done, but before rushing off, it is important to be sure it is the case.

    M.

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines