Pat testing - low insulation reading

[tomodo]

Hi all, recently pat tested abit of equipment, it contains 24v power supplies, a frequency inverter, relays and a motor, its on a 13amp plug so requires pat test, however we get a low LN to E reading unless we disconnect the inverter. Reading is 0.9Mohms, is this normal or should you still requires the minimum 1Mohm resistance to earth. Thanks

 

[westward10]

Have you tried the test at 250v?

 

[tomodo]

We will do but doesnt it need to be a 500v test LN to E?

 

[westward10]

There are possible filters within it which are being triggered by the 500v.

 

[tomodo]

Tested at 250 but still low resistance 0.9

 

[westward10]

I think this would need the manufacturer's input either by you or the client.

 

[tomodo]

I have just spoke to them on the phone they dont seem so sure either :/ waiting on a message back. Surely it needs to be above the minimum 1Mohm to be satisfactory even just testing at 250v dc?

 

[westward10]

Does your tester perform an earth leakage test?

 

[James]

I have known some inverters to be damaged by insulation testing.
as a general rule, i tend to avoid doing an insulation resistance test on things like that, check plug and cable but disconnect from internal electronics.