Hi-Pot testing

Hi guys,

We use the Associated Research Hypott III Model 3665 and it runs about $2k but I think you can only get newer models now.

As you probably know, Hi-pot testers are good devices for verifying there are no shorts to ground in the product or breakdowns in insulation materials such as wiring insulation, fiche paper, plastics, caps, etc.

I suggest a great degree of caution whe considering hi-pot testing.  You will be injecting thousands of volts into products which can jump over to grounded surfaces or yourself.  You must verify that your bench ESD pad is disconnected and that you are not grounded through ESD wrist or foot straps as well.  Some items of some electronics products can be destroyed by improper testing.  You must also know whether to use AC or DC voltage, what the voltage should be, what ramp time used, and what dwell time.  If not, then you may achieve a false fail indication.

We do hi-pot test virtually everything we make.  Source 4s, dimmer modules and racks, ELTS2s and other power products are most critical.  We also test contral products and cabinets and LED fixtures.  I can't right now think of what we don't test.  Oh, and hi-pot tests are different to some degree depengin on the product (voltage, rise and dwell).

While testing would be nice to do after a repair, I'm not sure we're quite ready to help you set up such a rig.

Let me know your thoughts.

David

My thoughts were not so much into the electronics side of things (i.e consoles, CEM's, automated lights,) but much simpler such as cabling, power adapters, etc. 

What I've seen commented on in other forums from other parts of the world is related more to the annual inspection of portable cables and fixtures to make sure the grounding is sufficient on fixtures, and that there is no leakage of current from faults in the cable insulation.   I don't know if that is what Hi-Pot testing is for, as I'm not entirely sure what the term encompasses.   I look into this as I'm spending time on the phone or doing other miscellaneous work as I have time, so it isn't a high priority for me, but I'm still interested in finding out what others are looking into.

Hi-pot testing of things like cables, connectors and fixtures is actually something to be rather careful of.

When you hi-pot something you are applying a very large voltage (up to 2kV) across the insulation. If this is repeated too often, it can cause insulation breakdown, and paradoxically your safety test will make equipment less safe over time!

I suspect the annual inspection you've heard of from other parts of the world is like the PAT test (Portable Appliance Test) in the UK - http://en.wikipedia.org/wiki/Portable_Appliance_Test

This test does not apply the full hi-pot test of thousands of volts, rather a slightly-higher than usual voltage (typically 500V) between hot&neutral and ground to expose any insulation problems. It also runs high current tests through the ground to check for proper ground continutiy under a fault condition.

This test is carried out periodically on portable equipment in the UK; as far as I know there isn't an equivalent in the USA but there may be testers that do some of the same tests available.

My policy when I used to work in repair shops was to perform hi-pot tests only on new equipment (e.g. a cable I had just wired up), or equipment on which I had done really massive rework (rebuilding most of a dimmer rack), and otherwise just to do lower current/lower stress tests when doing smaller repairs.

Tom

This all started because I have some dimmer modules (some old EC 6K's) that were in a flood, and the customer needs rebuilt.  I'm a little worried about the lacquer insulation on the chokes, and the chance of them shorting to the choke's core.  My feeling is that just measuring the resistance between line, load and ground isn't going to be sufficient.  My understanding of Hi-pot testing (correct me if I'm wrong) is that it will expose any weakening of insulation.  I want to make sure that  the chokes are not just about to fail.  After all, the choke is subjected to a lot of physical stress (both magnetic and thermal.)

So I started to investigate. 

I assume (but what do I really know)  that the Hi-Pot test is putting hi voltage between line+ neutral and ground, and is only testing for faults to ground.

In the case of rubber cable, SO cable is rated to 600V.  Does that mean it is only tested to 600 volts?  Or does 600 volts require a test to 5 x the rating  or some other margin of error.  I also assume that the actual tests are dictated by a listing agency, such as UL.

This all started because I have some dimmer modules (some old EC 6K's) that were in a flood, and the customer needs rebuilt.  I'm a little worried about the lacquer insulation on the chokes, and the chance of them shorting to the choke's core.  My feeling is that just measuring the resistance between line, load and ground isn't going to be sufficient.  My understanding of Hi-pot testing (correct me if I'm wrong) is that it will expose any weakening of insulation.  I want to make sure that  the chokes are not just about to fail.  After all, the choke is subjected to a lot of physical stress (both magnetic and thermal.)

So I started to investigate. 

I assume (but what do I really know)  that the Hi-Pot test is putting hi voltage between line+ neutral and ground, and is only testing for faults to ground.

In the case of rubber cable, SO cable is rated to 600V.  Does that mean it is only tested to 600 volts?  Or does 600 volts require a test to 5 x the rating  or some other margin of error.  I also assume that the actual tests are dictated by a listing agency, such as UL.

In Bruce's situation, hi-pot testing does sound appropriate (in my experience water isn't too much of a problem for choke laquer, but overheating is bad news for it).

You're correct - a hi-pot tester puts a high voltage between the L&N (which are connected together) and the ground. Never a high voltage between L and N as that would obviously damage the electronics being tested! The purpose of the hi-pot test is to expose any faults in the insulation between ground and the "live" parts of the circuit in the equipment.

The voltage equipment gets tested at depends on the equipment and how/where it will be used. I believe that here at ETC we hi-pot US market (110V operation) equipment at either 1kV or 1.5kV and European (230V operation) products at 2kV.

The 600V on the jacket of a cable is usually the maximum voltage it is rated to carry under running conditions, rather than the voltage it's tested at.

-Tom