Can a 250 V IR test still damage equipment

[Barx]

No, this is isn't related to my last post. Well I guess it is related in the fact both are regarding IR tests, but I haven't blown anything up doing IR tests, lol.

If doing an IR test and are unsure if anything it left connected. Is doing a 250 V (L-N) to CPC test safe, even for 'sensitive' equipment?

Ta

 

[Lurch]

It probably depends on the equipment, it shouldn't see 250V between the live conductors and earth so it wouldn't be a great surprise if something did fail doing LN to CPC @ 250V.

 

[rapparee]

It probably depends on the equipment, it shouldn't see 250V between the live conductors and earth so it wouldn't be a great surprise if something did fail doing LN to CPC @ 250V.

I always assumed that this was safe, and 500vdc L-N was unsafe 

 

[ProDave]

I always assumed that this was safe, and 500vdc L-N was unsafe 

But if something was connected, then your  tester would not generate anything like 500V

 

[apprentice87]

Well, ok, so i am not an electrician, but i would have thought that if any particular piece of equipment [and i am talking class one stuff now] could not stand 250v to earth, it would be positively dangerous to use, being as how in use, it will see anything up to about 360V to earth..

This is presumably why 250v circuits are tested at 500v

john..

 

[Sharpend]

Doing LN-e at 250vdc shouldn't harm as the neutral side is designed to carry 240+/- volts, there will be no potential difference between L&N.   

 

[Lurch]

I worded that badly, what I meant was I wouldn't be surprised if a 250V IR test did affect something in a bad way. It shouldn't, but I am always wary.

 

[Sharpend]

 Now if you have the fluke 1664fc it will do an IR pretest to establish if anything is connected thus preventing any damage!!

 

[Barx]

 Now if you have the fluke 1664fc it will do an IR pretest to establish if anything is connected thus preventing any damage!!

Be interesting to know how that works....

 

[Bruspark]

250V between Live and Earth and  Live and Neutral are business as usual for any remaining connected devices

 

[Andy™]

250V between Live and Earth and  Live and Neutral are business as usual for any remaining connected devices

if you have a fault (i.e N-E short) then you will end up with the IR test voltage between L&N. at 250v i wouldnt expect any damage, but its possible

 

[Sidewinder]

It's 250 V d.c. limited to 10mA, any low resistance on the circuit from connected appliances and the voltage drops dramatically, and very quickly after connection.

This is patently obvious with the Fluke 156x & 166x series, I'm not sure about any others, as it gives you the actual test voltage along with the IR reading.

It's the current that is fixed and limited, by the IEC standard for the instrument, the voltage is designed to droop under load.

So, in the event of any real load being connected to a ring final circuit when it is put under test @ 250V I doubt that the voltage would actually ever reach that level in the first place, due to the current being taken by the load when across L & N.

As far as L&N to E goes, then the appliance will be seeing possibly 245V a.c. RMS under normal circumstances L - E.

WIth a typical peak as I type here, my power analyser is plugged in along side me of +/-364V wrt earth, RMS 237.4V, 49.93 Hz (FWIW).

So is a rise of 6% above "normal" voltage an issue, remembering that the RMS is allowed to be 230V +10% -6% so, 216.2 to 253, thus, IMHO I doubt that anything connected would suffer from a 250V d.c. applied voltage with a maximum open circuit current of 10mA.

 

[apprentice87]

My Megger 1730 gives the voltage as it tests too.. and you can choose from 100, 250, 500, or 1000..

john..

 

[Barx]

Can't I've noticed either way with this one tbh, will check it out on next use. Cheers

 

[phil d]

I don't know if it is the same now,but some years back a lot of stuff that could be damaged by an IR test came with a sticker that you stuck to the dis board. I remember fitting some rcd sockets and some smoke alarms that came with these, and iirc some dimmer switches too.

The dimmers had a sticker worded something like "warning electronic dimming devices which may be damaged by Insulation testing are fitted to this installation, remove before testing". 

We were always told to make sure we followed any such labels, as regards portable equipment we were told to get the client to go around and unplug everything, if he didn't and it got fried it wasn't our fault.