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[pscocoa]

A pond pump kept cutting out which means overheating and now will not work at all. Did a continuity test and it seems circuit is good - same with transformer. Am I making an error in trying to use multimeter for this purpose?

[Marks DTM Calib]

Any idea on the type of pump motor? (make/model may help).

When you say tripping out, is that the mains supply to the transformer is tripping or the transformer output?

[pscocoa]

No mains is not tripping- it is a very low voltage  water feature pump - 11va. When I set meter to continuity it reads 1 in left corner which is supposed to be fine. When testing circuit I get beep which is also supposed to be ok.i have now fitted new pump and transformer and all is fine. I should have tested new pump with old transformer before I installed and put the heavy concrete bits back in place

[Doctor Gollum]

If you've replaced both and it is working again, then i wouldn't worry too much. You can always apply a modest voltage to the pump to test it so that you potentially have a spare, but I guess that depends on effort vs price.

If it was £2,000 then you'd have already checked it first, and if it was sub £50, then it's pretty much a consumable item, especially if it lasts more than a year

[pscocoa]

Yes - low cost - was more interested in understanding the continuity capability of my multimeter. Cannot seem to find a similar situation on the web.

[LC0112G]

Yes - low cost - was more interested in understanding the continuity capability of my multimeter. Cannot seem to find a similar situation on the web.

Continuity is effectively measuring the resistance between the probes, and expecting it to be less than a set amount - usually a few ohms. It's more useful for measuring wires/switches (that are supposed to be near 0 ohms),  than for motors which won't (shouldn't) be 0 ohms.

A large motor will have very low DC resistance, so may continuity check Ok. Similarly a filament light bulb. However, smaller motors, pumps and bulbs will have higher DC resistance and may not continuity check correctly.

What you DON'T want with any motor, bulb or lamp is a dead short - zero ohms. That indicates a short in the unit, and the wires may well emit some of their latent smoke if you power it up. There should always be some resistance.  You don't say what the supply voltage is, but an 11VA pump when running from a 12V supply will consume about 900mA, and so should appear to have a resistance of about 1.1 ohms.  This may or may not continuity check - depends on the meter.

It's a bit more complex than that - motors tend to increase in resistance as they spin up( reverse EMF and all that guff), so they'll read low resistance when continuity checking. But they shouldn't read zero.

 

[dave the builder]

pond pumps tend to be induction motors ,the impeller/armature is magnetic ,the stator windings are sealed and watertight   
so testing with a multimeter ,you may find the windings are fine and the fault is the pump is jammed ,seized impeller ,or bearings worn stopping the impeller turning due to no clearance .
most pond pumps come apart for cleaning for this reason
what make /model ?
you can get replacement impellers for most branded good quality pumps 

[Kevin Wood]

When using a multimeter on the Ohms ranges, 1 on the left hand side usually means it's an open circuit, which isn't good.

[dave the builder]

or I looks like a 1 due to the poor LCD digits  . I = infinity .  which is a lot and then some 

[pscocoa]

When I referred to 1 that is when multimeter is turned on without connecting to anything. So the 1 correctly shows open circuit. When I connect up it shows a reading other than 1 with a confirmatory beep that all is well. I suspect Dave's point on internal workings is probably the relevant area. As said there is a thermal cut out on the pump and an isolator feature on the transformer. Thanks for all the input.