Insulation resistance

[Regs]

Getting really low insulation res. readings from my D.B.
Neutral bar to Earth bar 0.35 M.O
Line & Neutral to earth 0.35 M.O

So strange, R.C.D. DOES NOT TRIP!

Have tried removing main earth and this makes no difference

If any 1 could shed any light be great

Cheers.

 

[Marvo]

Firstly reconnect the earth immediately.

Can you give more detail on where and how you were doing the test and what tester and settings your using.

Does the RCD trip if you press the test button?

 

[jamesBoater]

Please correct me if im wrong but isnt the resistance still enough for the RCD to hold!

 

[Risteard]

So strange, R.C.D. DOES NOT TRIP!

Hardly strange, given that you have a resistance of 350,000 Ohms.

Therefore less than 0.0007A will flow. The RCD needs nominally 0.03A

 

[Regs]

Using a megger on 250v & 500v. Found one fault, when i disconnected the pond pump the reading has now gone upto 1.2 M.O. and have narrowed this second low reading down to the ring main between neutral and earth.

 

[Lucien Nunes]

Edit: ^^got there first

 

[Regs]

Hardly strange, given that you have a resistance of 350,000 Ohms.

Therefore less than 0.0007A will flow. The RCD needs nominally 0.03A

Ah O.K. cheers whats the formula you used here?

 

[jamesBoater]

simple ohms law

Ah O.K. cheers whats the formula you used here?

 

[44ALLAN]

Ah O.K. cheers whats the formula you used here?[/QUOTE]

No idea divided by several volts and adding 3 ohms over 2 amps............that should at least maim someone eh !! fgs?

 

[Des 56]

Hardly strange, given that you have a resistance of 350,000 Ohms.

Therefore less than 0.0007A will flow. The RCD needs nominally 0.03A

Slow down Risteard your getting to far ahead of the class

 

[Marvo]

Yep, the fault is too small to trip the RCD but I'd repair any fault under 1Mohm as a matter of course. If the fault has bee localised to a cble between 2 sockets then the cable may have been damaged or possibly there's damp in the sockets.

 

[Regs]

So when you do an insulation res. test before fitting an R.C.D. what minimum value would you be looking for?

Also would this now suggest my pond pump is on its way out or letting water in?

 

[Paultrim123321]

Mmmm Very Important Redhead?? Well that's how I remember it

 

[jamesBoater]

Surely with the 2391 under your belt this is stuff you should know !

So when you do an insulation res. test before fitting an R.C.D. what minimum value would you be looking for?

Also would this now suggest my pond pump is on its way out or letting water in?

 

[telectrix]

So when you do an insulation res. test before fitting an R.C.D. what minimum value would you be looking for?

Also would this now suggest my pond pump is on its way out or letting water in?

a reading over 1Meg. is acceptable, but it's good practice to investigate anything under 2 Meg. the pond pump could just be moisture in an adaptable box or outdoor socket.

 

[Regs]

Surely with the 2391 under your belt this is stuff you should know !

Yeah i know that of course. But if you add an RCD you are making the safety alot better you can't be held liable for a fault already in place. You could advise the customer and charge to correct it, surely?

 

[Regs]

a reading over 1Meg. is acceptable, but it's good practice to investigate anything under 2 Meg. the pond pump could just be moisture in an adaptable box or outdoor socket.

Yeah cheers, there is no adaptable box, i checked the socket. Insulation res. went up when i pulled the plug to the pump.

 

[telectrix]

Yeah i know that of course. But if you add an RCD you are making the safety alot better you can't be held liable for a fault already in place. You could advise the customer and charge to correct it, surely?

before adding an RCD you should test to see if there are any faults that will cause problems, along with earthing and bonding. you then factor the cost of fixing these faults as part of your quote.

 

[Marvo]

Any pumps but especially submersible types are prone to low insulation. Even slight wear on the shaft or seal coupled with the heating and cooling during normal operation and it's all over for the IR. If it's a small domestic pond pump then it's probably better to replace with new rather than attempt repairs.

 

[Octopus]

Doing an IR test with loads still connected is always going to end in tears.

 

[44ALLAN]

Hot motor /cold motor............summer /winter ambient temp lol.
Appliances just switched off or been standing for several hours.

The inexperienced will see faults that aren't there if their comparing results from previous tests

 

[Regs]

Doing an IR test with loads still connected is always going to end in tears.

Yeah i thought the load was removed so you don't fire 500v down your line and neutral and destroy items. Didn't realise, to be honest that items not in use but still plugged in would also still be a problem.

 

[LittleHelper]

Test between all conductors seperatley!! Probably a load!

 

[Brightspark2]

Check for more loads that are connected...or neons...FCU's etc etc

 

[Guest111]

Instead of disconnecting the main earth to the board,try disconnecting the L N E of the circuit you are working on and test them,it's just possible that even though you have disconnected the main earth that the bonds to gas and water may be affecting your readings.