insulation resistane testing please help

[paulthemagpie]

Insulation resistance testing hasbeen carried out on a installation in a shower block and the followingresults obtained

live to live = 200m ohms
live to earth = 0.5m ohms
a. are these testresults are acceptable:
b. The actions to be taken should thetest results be unacceptable are:

 

[DaveyD]

Hi Paul, what is your thinking on it?

 

[wallyanker]

Anything above 1mohm is acceptable, although I personally would like to see more than that.

Providing you have disconnected all sensitive equipment, then you have an issue with the insulation breaking down between live and earth. The section of cable at fault will need to be replaced.

 

[paulthemagpie]

Hi Paul, what is your thinking on it?

my thinking was live to earth has an issue as reading is low

 

[ackbarthestar]

A couple of questions
1/ What was the result of N-E ?
2/ How many circuits are you IR testing in the shower block?

As it stands, it needs further investigation and testing

 

[topquark]

There isn't much acceptable about either reading expressed in MilliOhms(m), I take it you mean MegOhms(M)!

 

[topcat]

Has as been said the result look poor live earth have you checked for neons if their is one then it will need to be isolatted so have a good look round see if their is one the retest with it isolatted

 

[paulthemagpie]

would neons the fact if they were neons that had not been discoonected cause this result to be too low?

 

[telectrix]

yes. because you are leaving a load with a finite resistance across L and N.

 

[topcat]

well said telectrix could test rn to earth as has been said and check results.

 

[paulthemagpie]

thanks, is they anything else that could cause a low reading?

 

[ackbarthestar]

would neons the fact if they were neons that had not been discoonected cause this result to be too low?

Neons are usually connected across the L-N of the load side of the DP Isolating switch and register a value of around 0.2M Ohms, not L-E. If the DP Isolating switch is off then it shouldn't register at all.

 

[Taylortwocities]

Yes but a neon would not be across line and earth, unless its been installed by a cowboy.
Not sure of the effect of a neon, as IR tests are done with DC........

In any case, Paul.
This is obviously a college exam question, so you should be able to come up with an answer first. We could then give you some guidance. You'll not learn by just asking without making any effort.

*CLUE*
Have a look in BS7671 in teh section on IR testing and what the acceptable IR limits are. then you could come up with an informed answer.

 

[paulthemagpie]

so basically the actions the need to be taking is they needs investigating to find what is causing the results to be low. which something such as neons not disconnected before test. if we find what we think is causing it we need to disconnect it and do the test again until we get the reading over 1 mega ohms

 

[Taylortwocities]

thanks, is they anything else that could cause a low reading?

Examples: WATER leak, dead mouse, dead plumber.

 

[topcat]

Yes poor cable instulation damaged cable poor connections at switch or in the shower unit if its a electric type damp cable. loads of stuff but would need investigation as has been said are you new to testing it can take some getting your head a round hope I have helped.

 

[paulthemagpie]

would surge protective devices cause the test to show low result?

 

[Richard Burns]

SPD s can cause low line earth IR results and if they are class three can then be damaged by a 500V test since class three operate at 400V.
Make sure all sensitive equipment is removed from circuit before testing and (not according to the regs) test at 250v first, if you get a low result check the attached items again.

Neons tend to produce an IR value of about 0.1Mohms or 0.5Mohms Line to Neutral depending on type.

 

[1shortcircuit]

My most recent fault finding turned out to be a failed Fused Connection Unit.

Went down the route of "divide and conquer" found the area causing concern, disconnected terminations and results were great??? Connected accessories and tested again and fault was back. Removed accessories and tested between terminals of Fused Connection Unit and sure enough the fault was there. Replaced with new unit, retested continuity and IR and problem solved. :thumbsup

 

[ackbarthestar]

Make sure all sensitive equipment is removed from circuit before testing and (not according to the regs) test at 250v first, if you get a low result check the attached items again.

Read more: http://www.electriciansforums.net/e...tane-testing-please-help-2.html#ixzz1zknxHu00
​

I think you'll find that there is a note to the IR test values where BS7671 states that 250V is permissible if you suspect that there SPDs installed.

 

[telectrix]

Examples: WATER leak, dead mouse, dead plumber.

i prefer the last one. need to test at 1000V, make sure he's dead.

 

[dagrat]

And if they are still moving after that, large lump hammer will do the trick!