# float switch passes continuity but still leaking voltage



## mburtis (Sep 1, 2018)

So maybe this is something common that I just don't know yet. Had a pump station acting up lately with three pumps on an alternating relay. It has a shut off float, a lead float, and two lag floats, and it was acting like the lead float was stuck on, but I tested continuity and it passed. I voltage checked it and I was getting like 100 V through it when it should have been off. Finally hooked it up to the megger and was getting around 1.5 Mohms at 250V. Checked one of the other floats that was working and got 150 Mohms. Is it common to have float switches pass continuity tests but still leak voltage through due to the nature of the construction?


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## splatz (May 23, 2015)

Something is wrong here, one tester or the other has to be wrong, if the test was done the same way. Did you completely disconnect the lead float to test continuity? I am thinking the controls may latch when the float activates and if you tested it in circuit you'd see continuity, but it would be through the latching not through the float.


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## joebanana (Dec 21, 2010)

Alternating motor starters are tricky. You've got to really know how they work. Could be a bad relay.


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## Cow (Jan 16, 2008)

Floats can do funny things when they get a little water inside them.

Sometimes I will meg them to satisfy my curiousity, more often than not though, I just change them and the problem goes away.

This assumes you have a thorough knowledge of the system and don't have a relay issue or didn't isolate the wires properly when testing, etc like the others mentioned.


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## gpop (May 14, 2018)

capacity coupling on a float wire which can be read with a high resistance meter would give you a false reading.

Any reading that's not 120v is always suspect unless you know that you have a load on that wire. 

If you tell us what the station is doing we maybe able to tell you what to look for.


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## mburtis (Sep 1, 2018)

When I tested both continuity and with the megger I had the wires disconnected so I was just testing across the float. I thought maybe the goofy voltages I was seeing was something to do the electronic nature of the alternating relay or there was something else wrong in the control circuits. As I was seeing 20-50 volts on the other floats in the open position as well but they seem to operate right. At first I thought the alternating relay was bad, because one output was always active, in other words it was always calling one pump to run regardless of the float positions, although the low water float will still shut them off but then it will restart the pump immediately when the low water floats rises. But then I unwired the lead float and wired one of the other ones in its place and it started behaving correctly. Initial issue we had was overloads and fuses blowing on the pumps. I'm thinking that it was pumping down and then just sitting at the bottom kicking on and off as the water sloshed right at the shut off level until it tripped. Confused the hell out of me as the switch showed open but then I was still getting voltage through it. A factor of ten difference in the megger reading between the questionable float and one that seemed good seems pretty conclusive though.


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## Quickservice (Apr 23, 2020)

Cow said:


> Floats can do funny things when they get a little water inside them.
> 
> Sometimes I will meg them to satisfy my curiousity, more often than not though, *I just change them and the problem goes away.*
> 
> This assumes you have a thorough knowledge of the system and don't have a relay issue or didn't isolate the wires properly when testing, etc like the others mentioned.


My first thought... replace the sucker.


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## gpop (May 14, 2018)

mburtis said:


> When I tested both continuity and with the megger I had the wires disconnected so I was just testing across the float. I thought maybe the goofy voltages I was seeing was something to do the electronic nature of the alternating relay or there was something else wrong in the control circuits. As I was seeing 20-50 volts on the other floats in the open position as well but they seem to operate right. At first I thought the alternating relay was bad, because one output was always active, in other words it was always calling one pump to run regardless of the float positions, although the low water float will still shut them off but then it will restart the pump immediately when the low water floats rises. But then I unwired the lead float and wired one of the other ones in its place and it started behaving correctly. Initial issue we had was overloads and fuses blowing on the pumps. I'm thinking that it was pumping down and then just sitting at the bottom kicking on and off as the water sloshed right at the shut off level until it tripped. Confused the hell out of me as the switch showed open but then I was still getting voltage through it. A factor of ten difference in the megger reading between the questionable float and one that seemed good seems pretty conclusive though.


Megging a float to ground might work as a test but i wouldn't bother as 90% of float failures i have seen where the float is reading while hanging can be traced to the cable.

By its very nature a float bends the cable a few inches up the cable this leads to the internal insulation failing or the wire breaking. Now you start to get intermittent readings depending on slight movements. The outer jacket may still be in good condition so a meg will not spot the problem. (seems to be worse if you add the weights to stop the cables twisting)

I think you did a good job is swapping it with another float then replacing it.
I also agree that the overloads and fuses were probably caused by the constant starting and stopping of the pump due to the float problem.


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## JRaef (Mar 23, 2009)

gpop said:


> Megging a float to ground might work as a test but i wouldn't bother as 90% of float failures i have seen where the float is reading while hanging can be traced to the cable.
> 
> By its very nature a float bends the cable a few inches up the cable this leads to the internal insulation failing or the wire breaking. Now you start to get intermittent readings depending on slight movements. The outer jacket may still be in good condition so a meg will not spot the problem. (seems to be worse if you add the weights to stop the cables twisting)
> 
> ...


 ^^^^ This. 

I've seen this several times. The float cable has flexed one too many times and the internal insulation has started to fail between the conductors. On one that I took apart, you could see little strands of copper poking through.


What happens is that in effect, your Stop float at the bottom becomes the Start AND Stop float. The reason you have both is because once the pump Starts, it runs until the Stop float drops out, preventing short-cycling when there are waves or turbulence. With the Start float always made, the Stop float will bounce and cycle your starters on and off rapidly. 



You will want to check the contacts on those starters, this sort of thing can cause them to burn up rapidly.


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## mburtis (Sep 1, 2018)

JRaef said:


> ^^^^ This.
> 
> I've seen this several times. The float cable has flexed one too many times and the internal insulation has started to fail between the conductors. On one that I took apart, you could see little strands of copper poking through.
> 
> ...


I'm fairly confident what you describe is exactly what was happening causing the overloads and fuses to blow. It was running down to low water level and then just sitting there bouncing on and off until it tripped something. I guess the insulation in the cable going bad would make more sense then the actual switch it self going out. Planning to change the float Monday and then I'll know for sure.


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## splatz (May 23, 2015)

I am not sure I follow. Do you wire your floats the way you'd wire momentary pushbutton switches? For pump down the high float starts and the low float stops...


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## mburtis (Sep 1, 2018)

splatz said:


> I am not sure I follow. Do you wire your floats the way you'd wire momentary pushbutton switches? For pump down the high float starts and the low float stops...


Essentially yes that's how this system works. The low water float is acting like the stop button. I can take a picture of the schematic Monday, took me a minute to figure it out.


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## splatz (May 23, 2015)

mburtis said:


> Essentially yes that's how this system works. The low water float is acting like the stop button. I can take a picture of the schematic Monday, took me a minute to figure it out.


The reason I ask is because if you treat the floats like momentary switches - even though they are not really supposed to operate that way - there should be less chaos from an intermittent bad contact or the float wobbling close to the tipping point.


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## 460 Delta (May 9, 2018)

splatz said:


> I am not sure I follow. Do you wire your floats the way you'd wire momentary pushbutton switches? For pump down the high float starts and the low float stops...


That’s maybe a better way than I handled a similar situation at a R-mix plant at a former employer. It was a fill up and shut down situation that sometimes would short cycle, so I set the float lower in the tank and let it control an off delay TDR. The tank would then “overfill” from the off delay to where it had been set before, seemed to work well enough. Yeah me and my TDRs!

I left no drawing and soon moved on to another job, does that make me a bad person?


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## Jlarson (Jun 28, 2009)

That's what they do when they start to go, either from the flexing or water intrusion.


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