Discuss 'No trip' function. High readings?? in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

S

Silk6911

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:  American Electrical Advice Forum

Hi guys just joined.

Using Megger 1553 multi tester. Great tester but when using the no trip function to get my loop imp reading through an RCBO the readings are really high...15-20 ohms?

Any ideas. I believe this is a common complaint on a lot of testers?

Cheers
 
SuperlecDirect - ElectriciansForums.net Electrical Suppliers
This official sponsor may provide discounts for members
P

PAUL M

  • Thread Starter Thread Starter
  • #3
i have metrell multi tester and i have the same problem,i was told because it uses less current to do the test in order not to trip the rcd it is slightly less acurate,its like if you mearured a football pitch with a 1 inch ruler or a ten foot ruler the smallest method of measurement will be less accurate thats the analogy i was given by manufacturer.
 
S

Shakey

  • Thread Starter Thread Starter
  • #4
Hi guys just joined.

Using Megger 1553 multi tester. Great tester but when using the no trip function to get my loop imp reading through an RCBO the readings are really high...15-20 ohms?

Any ideas. I believe this is a common complaint on a lot of testers?

Cheers
well this is common but it doesnt matter

as long as the reading is 1667 ohms or less, it complies;)
 
S

sparkyork

can somone explain something: in the regs theres the table outlining max earthloop readings etc for varying mcb's, fuses etc.....so if you gotta circuit who's Zs should be below say 1.7 ohms then whats this 1667 ohms all about??

really confused? does this mean that loop readings on circuits are pretty much redundant?
 
S

Shakey

  • Thread Starter Thread Starter
  • #6
can somone explain something: in the regs theres the table outlining max earthloop readings etc for varying mcb's, fuses etc.....so if you gotta circuit who's Zs should be below say 1.7 ohms then whats this 1667 ohms all about??

really confused? does this mean that loop readings on circuits are pretty much redundant?
A subject close to my heart Rich, the answer is pretty much yes for RCD protected circuits.

1667 ohms is the result of dividing 50V by the trip curent of 30mA. (50V being the maximum safe touch voltage)

so what we are saying is, if the Zs is 1667 ohms, when the fault current reaches 30mA, the RCD will trip, and at this point the maximum fault voltage that can occur will be 50V. And of course the Zs is likely to be a lot lower, so the fault current will be a lot higher, and the trip time a lot quicker.

So under the 17th, with pretty much everything on a 30mA RCD, reading 1.7 ohms, or 2 ohms, or any value less than 1667 ohms is pointless because the RCD will trip long before the MCB (for earth faults)

I did a post entitled "will Zs readings be redundant under the 17th edition" or something, and we batted this one about for a while, might be worth you checking it out:)
 
S

sparkyork

cheers shakey ill check that post out, before i go forum surfing tho, on the new 17th certs is the max Zs box going to be 1667 then, so long as theres n RCD supplying said circuit?
 

Reply to 'No trip' function. High readings?? in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

Top Bottom