Application of E stops

[johnboy6083]

Hi gents.

Recently io was involved with a booster pump upgrade for a subcontractor of a water company. My involvement was the electrical installation, including instrumentation.

this pic is of the setup.


pump 1 to the left and pump 2 to the right
my question is about the e-stops. the two estops are behind the pumps, and there is one for each pump. Both are labelled e stop one and e stop 2 respectively.
the only other e stop for this system is on the main panel which is about 2m left from where im standing taking this photo. there is a cubicle per pump, and an e stop on the door of each cubicle.
my problem is that each e stop only stops the pump for which it is lablelled. i think this is wrong, as in the event of say an operative getting his hand caught on the shaft of the motor, and me running to push the e stop, in my panic, i may press the wrong one, and wait a few secs before i realise my mistake.
I beleive that the e stops should cut out both pumps, and kill power to all of the circuits that belong to this system.
is this covered in PUWER?
what do you lads and ladies think?

All comments appreciated,

John

 

[SirKit Breaker]

I agree, the e stops should kill power to the complete system and also drop any other power supplies out like air or hydraulics. That was how i had to wire them in my last life, and they also had to have a reset system so power could not be reinstated without pressing a reset switch of some type. But it s been a while for me, so dont accept my word on it.

Cheers.......Howard

 

[johnboy6083]

thanks for your reply howard.
the system does have to be reset before power can be restored.
i garee with the rest of your post.
is there any specific legislation or regualtion that refers to this?
also when testing a system like this, is there any additional paperwork outside of 7671 sheets that should be completed?

 

[SirKit Breaker]

I would be looking at the Electricity at work regs, and the Health and safety at work act. There is also the G4 machinery guarding standards, which i am fairly sure covers all this plus interlocking guards and so on. It will all be in there somewhere, but just where i dont know. The paperwork will be normal 7671 stuff, as there is no other electrical paperwork. If you are not too sure, then dont be afraid to ring your local Health and safety executive and get some guidance straight from the horses mouth so to speak. I have not done much on this stuff for a good while, with the odd exception replacing like for like switches etc.

Cheers........Howard

 

[johnboy6083]

the problem is that im effectivley employed (via an agency), and this issue was raised by myself to my supervisor, who told me not to worry about it. I think that this may of been down to the fact that the design engineer is a friend of his. at the moment this job suits me very well, and i dont want to do anything that may compromise that.

 

[sparx24]

My take on this would be as long as labeling is unambiguous it's fine as is.
Suppose the set up was much more complex eg many pumps, such as in a power station or large water treatment plant or boiler/plant room, it would be potentially dangerous to 'kill' the whole plant for a problem with one pump,
eg total loss of boiler feed water or gas circulation in a nuclear power plant!
If machinery correctly guarded, no contact with moving parts should be possibly anyway.

 

[silva.foxx]

Would you say the pumps together form a common system?

Is there any complication than can become apparent should both systems needlessly become "emergency stopped"? ie flooding?

 

[johnboy6083]

the 2 pumps are both part of the same system. one pump is redundancy. they run of a rotation of 36 hrs i seem to remember. they are not critical, as they are only booster pumps, supplying water to Holtye in E Sussex. the water can flow without the pumps, but not at a great pressure.

 

[silva.foxx]

Personally I think if they're a system then the estops should be common to both pumps!

Great document: http://www.hs-compliance.com/uploaded/documents/THE EMERGENCY STOP.pdf

 

[Knobhead]

Many systems like this have auto start of the standby unit. So if you press the stop on pump 1, pump 2 starts. It also leads to people using stops instead of correctly isolating the drive.

Neither a good idea!

 

[johnboy6083]

this is exactly the case tony. i dont like the idea. its handy for convenience of the water company though!

 

[silva.foxx]

Many systems like this have auto start of the standby unit. So if you press the stop on pump 1, pump 2 starts. It also leads to people using stops instead of correctly isolating the drive.

If the units form a system then it should be treated as a system... if a common pipe splits or a joint blows... the estop should stop the system.

An operative getting his hand caught on a motor shaft is likely to be a behavioural issue (ie. correct lock-off!), although all guarding should be in place with correct fixings.

The awkward bit is the separate panels for a 'commoned' system... but that can be worked around.

 

[Knobhead]

Many systems I’ve worked on have had a “master” E-Stop system. Any P/B stops the lot. One particular system was an absolute pain 15 MCC panels spread over 6 floors each had to be reset individually.

One thing to watch with this or any system is that hydraulics and pneumatics fail safe.

 

[brightspark66]

i have worked quite alot on pressurisation equipment on high temp hot water systems.a very similar set up to this, two pumps etc.the pumps run on a rotation system when required,but when one pump is running and the demand is high the second pump kicks in as a booster pump.As all this is one system in my opion all the e stops should cut everything out.Of course to comply this would then need manual reset.

 

[vaughant]

Many systems I’ve worked on have had a “master” E-Stop system. Any P/B stops the lot. One particular system was an absolute pain 15 MCC panels spread over 6 floors each had to be reset individually.

One thing to watch with this or any system is that hydraulics and pneumatics fail safe.

I`d agree with this,can be a pain in the rear but I would certainly expect this system to cut both pumps out,it`s not that hard to wire in,perhaps you could use the dreaded Pilz relay or such like?
Strange this wasn`t done as it looks a very neat install otherwise?