Capacitors

[the pict]

I have installed a 3 Phase 12Kw twin tank fryer in a restuarant, nothing unusual there but, whilst I had the terminal cover off it was easier to undo the terminal bar and pull it out the way to get the cable into the stupidly small space attached in parallel to each phase terminals was a 0.6mf capacitor, other than some sort of current balancing I cant see what they are for, any ideas
Pict

 

[shanky887614]

no picture attached? would be useful

 

[Marvo]

It's more likely a noise suppressor to stop spikes when the elements are switched on and off.

 

[telectrix]

as marvo says. the caps help stop RF interference on TV and radios etc. good fun when they go short circuit.

 

[the pict]

Tel what happens if the do short,??
P

 

[Robotstar5]

Tel what happens if the do short,??
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They can go bang quite spectacularly!

 

[telectrix]

they explode. usually take out a OCPD. once exploded, the s/c has gone so ocpd will reset. had it loads on TVs in the 70's-80's. nice earners.

 

[the pict]

I use a few on refrigeration plant as motor start devices, never been around one when it went tho, usually the poor wee things fail and be sick all over they surrounding machinary,

 

[Besoeker]

I have installed a 3 Phase 12Kw twin tank fryer in a restuarant, nothing unusual there but, whilst I had the terminal cover off it was easier to undo the terminal bar and pull it out the way to get the cable into the stupidly small space attached in parallel to each phase terminals was a 0.6mf capacitor, other than some sort of current balancing I cant see what they are for, any ideas
Pict

Assuming you mean 6uF rather than 6mF I'm with the others here - noise suppression. If it's actually a supressor it may also include a resistor.

On big capacitor banks, we make some fairly large variable speed drives.
We looked at one a couple of weeks ago which has 192 off 2,200uF capacitors. They are in series/parallel strings with monitoring for voltage and current sharing to try to prevent the catastrophic domino failure - and that can really be dramatic.

 

[the pict]

Sorry yes uf, mf must be my agricultural heritage thinking of Massey Ferguson
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[Marvo]

Assuming you mean 6uF rather than 6mF I'm with the others here - noise suppression. If it's actually a supressor it may also include a resistor....

Yep, it's not uncommon for the device which usually looks like a normal capacitor to actually be a combination of components internally. If there's a resistor in it then it probably be of a fairly high value usually >1Mohm. The visual giveaway is if it's a suppressor or any other type of device that's installed between different phases or between phase and neutral or even between phase and earth then it have 'Class X' written on it. This distinguishes it from a normal capacitor like a motor start cap which would explode in very short order if it were connected directly across 230v or 400v. Because Class X capacitors and non-Class X capacitors often look so similar it's obviously very important you correctly identify these types of components before replacing them or altering the way they're wired.

 

[shanky887614]

Yep, it's not uncommon for the device which usually looks like a normal capacitor to actually be a combination of components internally. If there's a resistor in it then it probably be of a fairly high value usually >1Mohm. The visual giveaway is if it's a suppressor or any other type of device that's installed between different phases or between phase and neutral or even between phase and earth then it have 'Class X' written on it. This distinguishes it from a normal capacitor like a motor start cap which would explode in very short order if it were connected directly across 230v or 400v. Because Class X capacitors and non-Class X capacitors often look so similar it's obviously very important you correctly identify these types of components before replacing them or altering the way they're wired.

thanks for that snippit marvo, never mentioned anything like this when they were talking about resistors and capacitors when I was at college a couple years ago

 

[Marvo]

You're welcome and I'm glad you found it useful. If you Google 'Class X capacitors' you'll find info on the different suppressors, the way they're connected and the way they operate. These types of devices are using the CPC and the system earth as a path for functional current flow (not in its protective capacity) and are one of the reasons I advocate TT earthing systems should be far lower Ra values than the hundreds or even thousands or ohms that the UK regs allow. Without a low impedance earth path their functionality is severely impaired.

 

[shanky887614]

its interesting to learn and read about this kind of thing because in door access etc in used to having resistors across cores to detect if they have been cut etc

 

[the pict]

Well I tucked them away in the wee cubby they came out of
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