Is there a way to test a SPD without spending thousands ?

[vwes59]

I know there are many MFT's out there which can test SPD's, but they all cost thousands of pounds, and I personally can't justify that cost which currently isn't mandated.

However it would be nice to know that when I install a SPD that it will function.

Is there a way of testing such a device with a "standard" MFT, for example mine is a Kewtech KT63DL. I seem to have read somewhere that you can do a ramp test on an SPD to check that it functions ? If that's right, I'm pretty sure my Kewtech is capable of doing such a test.

 

[Dustydazzler]

I have never tested an SPD in my life

To me its one of those 'safety devices' you just install and forget about much like RCDs

 

[brianmoooore]

Thought these things self tested, with a flag changing from green to red when they've stopped the number and level of surges they're designed for.

 

[pc1966]

If you check at 250V they should be high R, probably well over 10M, but if you test at 500V it should be low, well under 1M. That big change in R versus V is basically how they work - a high voltage spike causes a lot of current to flow and so diverting it from the equipment normally supplied.

However, make sure your circuits are all isolated, etc, as 500V L-N can cause damage to low power electronics, as well as invalidating the test.

The N-E on some SPD might not conduct at 500V but will at 1kV, however, that is not something to do wired and just switched off due to the risk of damage to other stuff. Fully isolate the SPD if testing that.

 

[pc1966]

Just to add some IR testers just tell you the R, but a few (like my MFT) also give you the actual voltage during the test. Typically for high R that is a bit above 500V but as it is limited to 1-2mA current it drops quickly below 1M or so. During a MOV style of SPD (typically for L-N use) you would expect to see something in the 370-430V region when it is tested,.

For a GDT (sometimes seen N-E) it is likely lower at 90-150V but as that goes sharp in to conduction when a high enough voltage is reached, and that can exhaust the MFT supply briefly, it can case a whining noise and higher average voltage reading as it cycles in and out of conduction.

 

[brianmoooore]

So what's inside these things? VDRs or is it more sophisticated with electronics?
What mechanism triggers the green to red flag?

 

[pc1966]

So what's inside these things? VDRs or is it more sophisticated with electronics?
What mechanism triggers the green to red flag?

Typically they are just a big VDR/MOV device. Sometimes it is a GDT for N-E (where no real risk of AC power follow-through) or a GDT and low voltage MOV in series to allow easier arc quenching if AC follow through is a risk, but still allowing a lower volt-drop per device so less heat for a given current waveform.

The status flag is normally a mechanical thing that is allowed to move if the VDR overheats and melts its solder connection, so that really is the "failure case" when it has had so much energy that it has allowed the joints to melt. For the wired PCB style there is no such overheating check but usually they have some sort of fuse in series that would blow on a big surge, where as the SPD seen in a CU is sometimes on a MCB, but quite a few just have the 60-100A DNO fuse as the protection of last resort and the let-through energy of that is enormous in comparison.

 

[Avo Mk8]

Deleted - better explanation above !

 

[pc1966]

In case anyone reading this has not seen them before:
SPD = surge protection device
MOV = metal oxide varistor
VDR = voltage dependant resistor (same as MOV, but not trade-name)
GDT = gas discharge tube

 

[Avo Mk8]

In case anyone reading this has not seen them before:
SPD = surge protection device
MOV = metal oxide varistor
VDR = voltage dependant resistor (same as MOV, but not trade-name)
GDT = gas discharge tube

Is MOV a trade name? I was under the impression that Varistor was a generic term, and from the various 'technologies' developed over the years, metal oxide has become popular.
Genuinely interested to know if I have been under a misapprehension!

 

[littlespark]

I have never tested an SPD in my life

To me its one of those 'safety devices' you just install and forget about much like RCDs

I put a “like” because I couldn’t find the “yer ‘aving a laugh” button.

Not testing RCDs? I’m shocked, Delroy.

 

[pc1966]

Is MOV a trade name? I was under the impression that Varistor was a generic term, and from the various 'technologies' developed over the years, metal oxide has become popular.
Genuinely interested to know if I have been under a misapprehension!

I had a feeling that is was trademarked in the USA by one of the manufacturers, but a quick look at Wikipedia suggests otherwise.

 

[timhoward]

I put a “like” because I couldn’t find the “yer ‘aving a laugh” button.

Not testing RCDs? I’m shocked, Delroy.

There’s a simple explanation - Delroy proved on YouTube he can’t figure out where the probes go.

 

[SirLouen]

To me its one of those 'safety devices' you just install and forget about much like RCDs

RCDs are one of the few devices that are thoroughly tested AFAIK (i.e. EICR)

I know there are many MFT's out there which can test SPD's, but they all cost thousands of pounds, and I personally can't justify that cost which currently isn't mandated.

The only problem I see with SPD is that testing basically mean killing the cartridges… They are not protection switches like MCB or RCD. What are you planning to test exactly?

If they work, they die, and you will need to replace them, meaning, that you will need to have faith again in the new cartridge (or the whole unit because occasionally they are not cartridge replaceable). This is like a car airbag. They cannot be tested, you have to rely on the right process of manufacturing and their certificates.

Although I'm uncertain if there are some SPD that have a switching option (probably just for permanent surge, not transient), instead of a cartridge because it's true I've also seen some testers that have a SPD MOV testing module like Kewtech KT66DL

This simply injects a surge and check when the SPD trips and shows you the trip V. Then you can check if the trip V is the same as the one that the SPD manufacturer gave you in the datasheet.

 

[brianmoooore]

You're not going to damage a MOV with a high voltage low current source, such as a MFT. It's when you ask them to pass hundreds of amps that they die.

 

[Avo Mk8]

This simply injects a surge and check when the SPD trips and shows you the trip V. Then you can check if the trip V is the same as the one that the SPD manufacturer gave you in the datasheet.

The test does not involve a 'surge'. The trip mechanism is generally a one-shot disconnect, as you'll see from post #7, so triggering the device is not helpful!
The test involves slowly ramping up the applied voltage (from a high impedance source), and measures the voltage at which the MOV begins to conduct, as you describe. That doesn't harm the SPD as the current involved is small.

 

[SirLouen]

The test does not involve a 'surge'. The trip mechanism is generally a one-shot disconnect, as you'll see from post #7, so triggering the device is not helpful!
The test involves slowly ramping up the applied voltage (from a high impedance source), and measures the voltage at which the MOV begins to conduct, as you describe. That doesn't harm the SPD as the current involved is small.

AFAIK, from what I've read, transients don't trip, only permanents. The only way to "test" transients is by breaking the cartridge on purpose. In fact, any transient SPD has a switch in the device, only the cartridge and a red/green indicator like @brianmoooore commented

How are you going to test this without breaking it?

 

[Avo Mk8]

How are you going to test this without breaking it?

Well it depends on what test you want to conduct. I was just referring to the test that MFT's typically carry out, which do not trip the SPD, but check that its MOV is alive and well.

 

[pc1966]

Exactly as @Avo Mk8 says, you can test the SPD is functional by using a MFT or IR tester, basically it should sustain 370-430V when tested at a higher voltage (i.e. 500V or 1kV) and the power involved in that is trivial so no risk of damage to the SPD.

If you wanted to type-test the SPD to see if it can absorb X Joules of surge energy, etc, as per the data sheet then it could very well be destructive, but that is far different from verifying it is present and connected as expected.

 

[pc1966]

I had a feeling that is was trademarked in the USA by one of the manufacturers, but a quick look at Wikipedia suggests otherwise.

I found a data book from around 1987 that shows I mis-remembered it, the trademark was for GE-MOV and not the generic Varistor or MOV notation: