Motor cable - style question

[Lucien Nunes]

I'm about to replace the cable from a starter to an existing 2hp 3-phase 3-wire motor adjacent. The motor is rigidly bolted to a bed and has a direct shaft coupling, i.e. it is not on slide rails. Normally, I would use stranded singles in steel conduit with a flexible conduit link to the motor, not least because the motors are usually larger and 6-wire. In this particular situation it is more convenient to use FP because that can easily pass through the structure.

The obvious thing to do at the motor end is to make a loop of FP and take it straight into the motor terminal box, but for no obvious reason this feels cheap. Maybe it's the FP's solid conductors but you would do it with MI which is even more solid. The alternative is to terminate the FP into an adaptable box adjacent and make a loop with flexible conduit and singles, which adds a set of connections but for some reason feels neater. In other circumstances there might be an isolator in this position but as the starter is 1m away and has one itself there's no point fitting another. WWYD?

 

[westward10]

Seen plenty of MI looped cables at motors but not sure I would use FP as the loop, unless supported would be 'floppy'.

 

[freddo]

FP is a terrible cable, anything else has to be better! I'd be mostly worried about mechanical damage to the FP during motor maintenance activities. I guess you could sleeve it with Kopex or similar in the area near the motor to provide some protection. I'd also be worried about the solid cores fracturing over time with vibration, but as above I've seen loads of MI connected motors and those solid cores and rigid copper sheaths seem to last ok.

Use MI, it's way cooler than FP, you know you want to...

 

[timhoward]

Maybe Flexi shield? and a few more words.

 

[marconi]

Product details - https://www.sab-cable.com/products/servo-motor-cables/sl-801-c.html

chainflex® motor cable CF885 - https://www.igus.co.uk/product/1087?artNr=CF885.15.04

These brands of motor connection cable have good specifications for exposure to oils, chemicals, vibration, temperature, sun radiation. They remain flexible at low temperatures if that is important for your application.

 

[David Prosser]

I think i would go with H07RN.

 

[Lucien Nunes]

I keep various chain cables and H07 in stock here but this application doesn't need flexibilty as such. We recently slid the motor back to replace the drive coupling but that was possibly the first time it had moved since the mid 1930s when it was installed. My point is not that it needs any special treatment, but that I don't think I've ever connected a motor directly to FP before and it felt cheap and nasty.

Use MI, it's way cooler than FP, you know you want to...

Yes, I should have specced that in the beginning. The existing feed to the starter is MI too. I have a roll of 4L1.5 which would do perfectly but it's a long way away. I haven't done any actual install for the best part of a year and it's proving to be a challenge to get the normal bits together so I'm not looking to make it any more involved than it needs to be.

There might be a plan B here, in that the starter looks to be going a bit further away from the motor than I visualised. In which case I will put a rotary isolator right next to it and make the final link in steel Adaptaflex and singles.

 

[marconi]

Someone had to ask - may we have some pictures please? I bet there is an interesting back-story to tell.

 

[Mike Johnson]

In the past when I have needed flexibility in cable runs with some protection from mechanical damage I'v used aircraft Kevlar braided cable sleeves, available in all sort of size's and colours: Kevlar Braided Sleeve Cut Resistant Hose Cable Protection High Temperature and Heat Resistant - https://www.abthermaltech.co.uk/kevlar-braided-sleeve-cut-resistant-high-temperature-heat-resistant-wire-cable-hose-tubing-protection.html

 

[Darkwood]

I would say vibration is the key concern to consider, stranded cables are easy to terminate with lugs and are flexible, any solid drawn is a no no for me, a joint box and as mentioned earlier, some ho7rn-f which suits most oily environments.