Control Of 1/2hp Motor Using 20a Sp Switch

[happysteve]

The sleeving of an identified earth is not acceptable again on paper...

You got a Reg number for that, darkwood? I've been struggling to find one.

514.4.2 says, "Single-core cables that are coloured green-and-yellow throughout their length shall only be used as a protective conductor and shall not be overmarked at their terminations, except as permitted by Regulation 514.4.3." This is not the case here. So I would have no issue with this, provided the core was suitably identified at both ends.

Unless you're referring to regulations or guidance other than BS7671?

~tin hat on~

 

[Darkwood]

I was refering to that reg' Steve, my wording wasn't the best but I did say in a flex it would be bad practice hence no exactly against any reg... Tin hat off

 

[happysteve]

Ah, fair enough Thanks for the clarification, always happy to learn.

 

[marconi]

Rather than placing the contactor adjacent to the motor what about co-locating a small solid state relay(SSR)
with the DP switch? The DP switch would need to make the neutral pole first and break it last for what I am about to suggest. The neutral pole is used to supply the SSR with the line feed. The line pole is used to switch the SSR. The line pole derives its supply from the output of the neutral pole. With this scheme all load current switching is done by the SSR.
For SSR see https://www.rapidonline.com/Catalogue/Search?filterSearchScope=1&filterCategoryPathROOT=Relays+&+Solenoids&filterDiscontinued=False&filterCategoryPathROOT/Relays+&+Solenoids=Solid+State+Relays&sourceRefKey=RAhiSQZjx&keywords=*
Randomly switched SSRs are recommended for inductive loads but one manufacturer at least says its zeroswitching range are satisfactory when load PF is better than 0.7.
For thermal overload protection affix one of 1,2 or 3 below to the motor in series with the line;
1. thermal cutout https://www.rapidonline.com/pdf/61-2078.pdf
2. thermal fuse https://www.rapidonline.com/pdf/61-2078.pdf
3. thermal switch https://www.rapidonline.com/Catalog...cs&sourceRefKey=_l0TBFqnG&filterSearchScope=1

 

[Lucien Nunes]

An ingenious scheme but not one I could use in practice due to the non-standard configuration and lack of space to fit the SSR. I would also have to switch the neutral to the SSR input as I need the neon indicator which is tied to the load neutral terminal and I doubt the existing switch has sequenced neutral pole operation (although new MKs for example do have). If I were going to make any significant changes I would simply replace the whole lot, but as I say it's difficult to access, difficult to put anything but a 1g accessory where the switch is and evidence is that the existing switch has worked for years or decades. Re. overheat prevention, it's not practical to attach anything to the motor, therefore detection must be based on line current via a motor circuit breaker or thermal overload relay.

 

[marconi]

This morning I have put a query to Honeywell/MK electric technical desk asking for them to provide the inductive switching rating of their grid switch MK4896N and to confirm its neutral pole is first make and last break. I thought of a grid switch so you could put a neon beside it all in the space of a standard switch plate.
I will let you have MK's response when I receive it. Enjoy the sunny weather.

 

[marconi]

Lucien, here is the response from Honeywell/MK on my query. Helpfully, they have given a contact number and invitation for further clarification. I cannot quickly turn up what is the definition of the AX rating - something for me to do in a quieter moment later.

We confirm that DP K4896N switch is specifically designed to make first / break last on the Neutral pole. In regard to Inductive loads the switch is AX rated and therefore meets the requirements of the standard BS EN 60669-1 which includes loads for Fluorescent lamps but not specifically motor loads having much higher start currents. For any further clarification please call our help line on 01268 563720 and one of our engineers would be happy to assist further with your query. Assuring you of our best attention at all times. (E&OE)

Stephen Cocks

Technical Sales & Service Department

Honeywell ED&S Ltd

The Arnold Centre, Paycocke Road, Basildon, Essex, SS14 3EA

Telephone 01268 563720

 

[Lucien Nunes]

Thanks for doing the spade work and forwarding that info. X-rated switches are those that do not have to be derated below their Ith rating for discharge lamp duty.

I did the job this afternoon and things were easier than expected. The motor was in pristine condition and newer than I thought - I tried to date it from the start capacitor but the date code was unintelligible - mid 1980s anyhow. The insulation resistance was >99MΩ both cold and hot and the leakage was <0.1mA starting and running. I fitted a motor circuit breaker / manual starter in an enclosure adjacent to the motor but left it as a standalone device with a 13A plug. There was enough room to add a separate enclosure in which I placed a small 20A contactor rated for 1.1kW motor load at 230V, to control the socket outlets like a glorified remote-controlled 13A strip. The cable to the switch had been successfully freed off and was replaced with 4-core, as the switch itself was replaced with a new decorative finish metal one that needed the earth. This overcame the colour code guilt with only the grey core needing to be sleeved blue for neutral.

The result is that the switch and indicator are normally wired, the motor and transformer are controlled by a contactor expressly rated for the duty, convenient local isolation and the ability to separate the parts remain by way of the 13A sockets, and the whole was completed in a few hours.

Cheers also to DW for the suggestions and ideas above!