Fixed Appliances

[Brad Ford]

Is it possible to carry out an Insulation Resitance test on "fixed wired" appliances (wall heaters, hand dryers etc.) without having to isolate or disconect the appliance?

I'm told that there is a Megger machine that can do this, but I've yet to find it.

Any help would be appreciated.

Cheers

 

[Andy™]

you cant do any dead tests without isolating the supply....

 

[m4tty]

You can test between (line and neutral together) to earth with the appliance connected. Obviously not live tho

 

[binky]

You can test between (line and neutral together) to earth with the appliance connected. Obviously not live tho

This is viable but not always very successful unless the appliance is at least turned off. Never heard of megger that can do this - check their website. They do a tester that doesn't trip 6A MCBs and 2 wire Zs tests without tripping RCD ( I know this cos they upgraded my test gear six months after I bought one )

 

[PBC_1966]

You can test between (line and neutral together) to earth with the appliance connected. Obviously not live tho

And then only if the appliance isn't connected as such, i.e. both supply conductors are isolated by a D.P. switch.

 

[a1spark]

Why is it you cant isolate or disconnect the appliances. ?.............If the reason is lack of access to their points of connection then you may test between line conductors and cpc on the circuit and note it as a limitation on the Report.

I imagine you would also have to consider your R1+R2 ,and Ze tests on these circuits.

 

[Brad Ford]

Thanks for the information.

 

[Ian Speirs]

And then only if the appliance isn't connected as such, i.e. both supply conductors are isolated by a D.P. switch.

You can test circuit with the appliance connected and switched on, "Dead test" and disconected from the db. Like m4tty said short the line and neutral together and test to earth. Its the same princible as portable appliance testing, the pat machine shorts out L + N together and tests to earth and asks for the appliance to be switched on first so it can test all the components are insulated from earth. The only problem is, this is the only insulation resistance test you can carry out. Appliances dont like 500v passing through them so no test between L + N.

 

[PBC_1966]

I took the original question to mean testing the insulation of the appliance itself. If you leave it connected to the supplying circuit you'll be measuring overall insulation resistance of the appliance and the fixed wiring (which if showing O.K. would be satisfactory).

But even measuring L-&-N combined to E, you'd still need to do some disconnection. Simply pulling the fuse or flipping the MCB off at the circuit's source won't be enough, as you'll still have an N-to-E path (unless it's a D.P. MCB, of course).

 

[binky]

I tend to connect L-N and test to CPC at 250V first and if it looks good, 500V second. Haven't killed anything yet:innocent

 

[Brad Ford]

Thanks again, much appreciated