Discuss 3 phase sub main…help please?? in the Industrial Electrician Talk area at ElectriciansForums.net

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Hi All
I’m in a bit of a quandary at work and need a couple of things clearing up if poss. I’m the maintenance manager/spark/fitter/skivvy/everything else that needs doing man 🙄 in a plastics factory and I’ve got to provide a supply for a new machine.

The current set up is a 90mm SWA protected by a 250a MCCB in the main distribution panel and is 30m in length to the first machine, then is paralleled into another isolator supplying a second machine (if that makes sense?).

We are replacing the first machine and I’m just not sure if it’s acceptable to piggy back from one machine to another? My instinct is that it’s not, but for the life of me, I can’t find anywhere in the regs to say that it’s not.

The machines have a combined power of 130kW, which works out at 335A and 90mm armoured is good for 251A using installation method E as it’s in traywork. This leads me to my second concern in that the cable isn’t rated high enough. It was installed before I started with the company and it has been running like that without issue, so before I go to my boss and tell him I need to spend £££’s on more cable etc, can somebody provide me a smoking gun, or better still, tell me it’s ok.

I haven’t had chance to measure the Zs readings, but I should be able to do that tomorrow during downtime.

Thanks I’m advance
 

Petej999

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Hi All
I’m in a bit of a quandary at work and need a couple of things clearing up if poss. I’m the maintenance manager/spark/fitter/skivvy/everything else that needs doing man 🙄 in a plastics factory and I’ve got to provide a supply for a new machine.

The current set up is a 90mm SWA protected by a 250a MCCB in the main distribution panel and is 30m in length to the first machine, then is paralleled into another isolator supplying a second machine (if that makes sense?).

We are replacing the first machine and I’m just not sure if it’s acceptable to piggy back from one machine to another? My instinct is that it’s not, but for the life of me, I can’t find anywhere in the regs to say that it’s not.

The machines have a combined power of 130kW, which works out at 335A and 90mm armoured is good for 251A using installation method E as it’s in traywork. This leads me to my second concern in that the cable isn’t rated high enough. It was installed before I started with the company and it has been running like that without issue, so before I go to my boss and tell him I need to spend £££’s on more cable etc, can somebody provide me a smoking gun, or better still, tell me it’s ok.

I haven’t had chance to measure the Zs readings, but I should be able to do that tomorrow during downtime.

Thanks I’m advance
Needs more thought than just measuring the ZS Mate, need to plan the entire installation, a shoestring bodge wont work and wont be safe, your boss needs to employ a decent contractor to plan, price and install, not a 5 min lash up as you plan
 

Petej999

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Hi All
I’m in a bit of a quandary at work and need a couple of things clearing up if poss. I’m the maintenance manager/spark/fitter/skivvy/everything else that needs doing man 🙄 in a plastics factory and I’ve got to provide a supply for a new machine.

The current set up is a 90mm SWA protected by a 250a MCCB in the main distribution panel and is 30m in length to the first machine, then is paralleled into another isolator supplying a second machine (if that makes sense?).

We are replacing the first machine and I’m just not sure if it’s acceptable to piggy back from one machine to another? My instinct is that it’s not, but for the life of me, I can’t find anywhere in the regs to say that it’s not.

The machines have a combined power of 130kW, which works out at 335A and 90mm armoured is good for 251A using installation method E as it’s in traywork. This leads me to my second concern in that the cable isn’t rated high enough. It was installed before I started with the company and it has been running like that without issue, so before I go to my boss and tell him I need to spend £££’s on more cable etc, can somebody provide me a smoking gun, or better still, tell me it’s ok.

I haven’t had chance to measure the Zs readings, but I should be able to do that tomorrow during downtime.

Thanks I’m advance
I see a suitable main switch on the incomer, busbar chamber after that suitable protection for all the other machine required, if you are just maintenance, then your knowledge of current rules and regs as well as installation methods may be limited, get a contractor involved, go to your boss with a decent proposal with costs proposals for work etc, not a weekend project like he wants.
 
OP
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I see a suitable main switch on the incomer, busbar chamber after that suitable protection for all the other machine required, if you are just maintenance, then your knowledge of current rules and regs as well as installation methods may be limited, get a contractor involved, go to your boss with a decent proposal with costs proposals for work etc, not a weekend project like he wants.
Fair comment mate. I’ve been in maintenance for 10+ years and have only just moved into this job. They are expecting me to just know and do everything, which we all know is almost an impossible task.

That’s a good suggestion though regarding going to him with a plan. They are just ordering new machines here there and everywhere and not really giving any thought as to how it’s going to work. I was only informed of this new machine last week and it’s arriving next week along with the commissioning team who will be expecting power ready to go. All this while I’m running a maintenance department 😐

I’m the first to hold my hands up when my knowledge isn’t up to scratch. The main incoming panel for the factory is only 1250a and they are running what I estimate to be 3000a worth of equipment (not all at the same time tbf, but it is a possibility). The place is a shambles, but as you say, all I can do is advise…it’s a tough one to deal with.

Rant over 😂
 

James

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I have had a lot of experience with plastic extrusion machines.
most of the time they will draw between 30% and 50% of there rated load.

the machine manufacturers when they are calculating what to put on the nameplate do the following
add up the load from all cooling fans, all heating zones, all ancillary sockets and the main motor.

this adds up to a huge number!
in practice, it will either be heating or cooling, never both at the same time, also when the screw is running it is hardly ever heating because of the frictional heat generated in the barrel. I have never seen one use more power (in total) than the rating of the main motor.

i suggest that you actually do a bit of current measuring when the machine is in operation and see what it actually uses, it is likley to be FAR less than the nameplate suggests.

P.s. the idea of doubling up a supply to 2 machines by looping in one isolator and then off to the next is not necessarily dangerous but not ideal either.
as long as the breaker supplying the circuit is not rated higher than the capacity of cable it supplies then it is ok in theory, but not best practice.
 

Petej999

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Fair comment mate. I’ve been in maintenance for 10+ years and have only just moved into this job. They are expecting me to just know and do everything, which we all know is almost an impossible task.

That’s a good suggestion though regarding going to him with a plan. They are just ordering new machines here there and everywhere and not really giving any thought as to how it’s going to work. I was only informed of this new machine last week and it’s arriving next week along with the commissioning team who will be expecting power ready to go. All this while I’m running a maintenance department 😐

I’m the first to hold my hands up when my knowledge isn’t up to scratch. The main incoming panel for the factory is only 1250a and they are running what I estimate to be 3000a worth of equipment (not all at the same time tbf, but it is a possibility). The place is a shambles, but as you say, all I can do is advise…it’s a tough one to deal with.

Rant over 😂
Good luck which ever way you decide Mate
 
OP
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I have had a lot of experience with plastic extrusion machines.
most of the time they will draw between 30% and 50% of there rated load.

the machine manufacturers when they are calculating what to put on the nameplate do the following
add up the load from all cooling fans, all heating zones, all ancillary sockets and the main motor.

this adds up to a huge number!
in practice, it will either be heating or cooling, never both at the same time, also when the screw is running it is hardly ever heating because of the frictional heat generated in the barrel. I have never seen one use more power (in total) than the rating of the main motor.

i suggest that you actually do a bit of current measuring when the machine is in operation and see what it actually uses, it is likley to be FAR less than the nameplate suggests.

P.s. the idea of doubling up a supply to 2 machines by looping in one isolator and then off to the next is not necessarily dangerous but not ideal either.
as long as the breaker supplying the circuit is not rated higher than the capacity of cable it supplies then it is ok in theory, but not best practice.
Thanks James, that’s really helpful. I was discussing with my apprentice today that we should measure the current for the whole factory, so it’s nice to hear that seconded!

I worked in automotive manufacturing before this so it’s about as far removed from that as you can get. Very challenging, but I’m gaining experience/knowledge everyday!

I was planning on running the 90mm cable to a TP+N 250a board with 2 160a MCCB’s supplying each machine in turn.

I must admit, I’ve done some calcs on paper and using the manufacturers data, the building is only capable of powering 1/3 of the load, but it’s still standing with no real issues of heat or overloading 🤷🏻‍♂️
 

Lister1987

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Fair comment mate. I’ve been in maintenance for 10+ years and have only just moved into this job. They are expecting me to just know and do everything, which we all know is almost an impossible task.

That’s a good suggestion though regarding going to him with a plan. They are just ordering new machines here there and everywhere and not really giving any thought as to how it’s going to work. I was only informed of this new machine last week and it’s arriving next week along with the commissioning team who will be expecting power ready to go. All this while I’m running a maintenance department 😐

I’m the first to hold my hands up when my knowledge isn’t up to scratch. The main incoming panel for the factory is only 1250a and they are running what I estimate to be 3000a worth of equipment (not all at the same time tbf, but it is a possibility). The place is a shambles, but as you say, all I can do is advise…it’s a tough one to deal with.

Rant over 😂
Be interesting to see 'as fitted' for the place, get a set of decent plans done if nowt else
 

Petej999

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Fair comment mate. I’ve been in maintenance for 10+ years and have only just moved into this job. They are expecting me to just know and do everything, which we all know is almost an impossible task.

That’s a good suggestion though regarding going to him with a plan. They are just ordering new machines here there and everywhere and not really giving any thought as to how it’s going to work. I was only informed of this new machine last week and it’s arriving next week along with the commissioning team who will be expecting power ready to go. All this while I’m running a maintenance department 😐

I’m the first to hold my hands up when my knowledge isn’t up to scratch. The main incoming panel for the factory is only 1250a and they are running what I estimate to be 3000a worth of equipment (not all at the same time tbf, but it is a possibility). The place is a shambles, but as you say, all I can do is advise…it’s a tough one to deal with.

Rant over 😂
Where are you situated? could come and try and sort something for you if not far from Northampton
 

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