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.

 

[Lucien Nunes]

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

Westminster’s rare Fyvie Hall pipe organ is being restored to its former glory

www.westminster.ac.uk

It's a little 2/4 Compton, much smaller than the instruments we usually work on but one that punches above its weight. It's the 3rd organ in Regent Street that my colleague Peter and team look after.

Blowers are usually conservatively rated, infrequently used and left unmolested, so it is not unusual to find old plant still in service. Average church organ blowers typically range from 1/2-2hp and are quite often single-phase. At low wind pressures it doesn't take much motor-power to make a lot of sound, hence the ability for a team of human blowers to blow even cathedral organs in antiquity.

In the late 19th and 20th century with large instruments voiced on higher pressures, the larger blowers got very large indeed. With our focus on concert and entertainment instruments we tend to meet units in the 5-20hp range and occasionally multiple blowers. As an example of the very largest schemes, the Royal Albert Hall has seven blowers totalling 62hp. My favourite blower is on my favourite organ, the Southampton Guildhall Compton. It's really three blowers in one, on a shaft totalling 12 feet long, which makes very efficient use of its 17.5hp.

 

[timhoward]

I wondered if it was for an organ!
There are one or two organs where additions have necessitated additional blowers. The Harrison and Harrison at Westminster Abbey comes to mind, which had a 5th manual / Bombarde division added.
The extra blower has it's own extra switch, which occasionally leads the to the inevitable happening - an extra loud solo stop becomes completely missing when the poor organist thought he'd turned it on and hadn't.
The blower switches are not always conveniently sited to correct such mistakes, in the case above they can't be reached or even seen from the bench.
For the huge cost of the work to extend that organ I always wonder that at a minimum a small indicator lamp wasn't provided to provide some reassurance!

 

[timhoward]

For anyone interested in the more extreme end of organ blower installation, this video, naturally from USA is quite an interesting watch

(the video image is a generator not a blower!)

 

[Lucien Nunes]

The Boardwalk Midmer-Losh is indeed an extreme instrument and a good example of a multi-blower installation where each serves a particular division and pressure. There is another multi-blower scenario where for economy when full registrations are not in use, and to avoid wind heating when the demand is low (which affects tuning), different-sized blowers are provided feeding the same trunk in parallel. For example, Hull Minster has a 5hp and a 10hp blower that can be started independently. For choir practice etc the 5hp blower is adequate and allows any stops to be played, but both need to be running to use full registrations.

Stand-alone motor-generators for the action DC supply (as shown in this video) were rare and only found on the largest instruments. Historically, many organs with electric action used a generator driven from the blower motor, and a few remain in use. In fact the Fyvie hall organ was running on its 18V MetVick generator until a few weeks ago, when a regulated power supply replaced it, on account of the new multiplex transmission (to allow the console to be moved and plugged in via a data cable instead of a 300-core snake.) Historically it was difficult to rectify high currents at low voltages and a generator was a reliable and effective solution. From memory the Boardwalk M-G set puts out 150A at 12V.

As usual, Southampton is an excellent example in original working condition unaltered since 1937. Its generators (there are two, one main generator and a separate exciter) are belt-driven from the blower and deliver 100A @ 18.5V with inbuilt voltage-drop compensation for the main cables using over-compounding. The peak load can be much greater (200-300A) for which the generator ramps up by a few volts to overcome the drop. I have written about this before and will probably do so again.

Pics later, I am supposed to be working

 

[Lucien Nunes]

Dave and I popped down to Regent St. yesterday afternoon to first-fix this. We opted for 4c 1.5 SWA from the starter, an additional isolator next to the motor, and tri-rated in 20mm Adaptaflex SP to the motor. The FCU for the 18V DC PSU is run in 3c 2.5 SWA.

Strictly speaking we didn't finish the first fix as we were let down by a couple of rogue 25mm couplers with incomplete threads. Parking anywhere nearby is impossible, even stopping to drop off is a challenge, so we went on foot and didn't have all the spare bits that would normally be in the van. It seemed a waste of time on a Friday afternoon to walk down to Berners St. just for conduit couplers, so I'll take some on Monday.

With the larger installations and where blowers are hidden away many floors below, etc, I tend to spec custom star-delta or soft starters often with symmetry monitoring relays, electronic overloads and ELV controls. But here there is just one control point adjacent, the blower is small and in-the-room, therefore I went with an off-the-shelf DOL unit by ABB with 230V control, adding a DP contactor for the 230V PSU.