3 phase Isolators current rating

[Pud]

Hi all,

Q for the electrical gurus amongst you.

We are moving factory to premises which was occupied by a rubber seal manufacturer. We are thermoplastic moulders.

They are leaving wiring which was supplied their machines - some of it is ideally sited for our purposes.

Our machines are rated at min 21.5kW and max at 45kW.

Isolators in new place are rated 63A and 125A*, and the question is will they be ok for the required loading(s).

* What is the max load that can be applied to this if we wanted a bigger press on it?

Sorry for being dim, but there is a lot of conflicting stuff on the interweb!

Cheers

Harry

www.tynevalleyplastics.co.uk

Politicians like to panic, they need activity. It is their substitute for achievement.

 

[LittleInch]

Voltage and number of phases would be good to know....

63A at 415V is a lot less power than it is at 3.3 kV....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ScottyUK]

Hi Harry,

I imagine that the load will be almost purely resistive because it will virtually all be electric heating elements, which means we can disregard power factor. That makes it a nice easy calculation, but yes it would be good to confirm voltage and phases.

Assuming it's 400V 3-phase you can get an absolute maximum of 43.6kVA out of the 63A circuit, and 86.5kVA out of the 125A circuit. I personally wouldn't run either right up to the circuit limits, and you'd need to check the capability of your upstream service from the leccy board - probably 3x 200A fuselinks, but not certain by any means.

 

[itsmoked]

What, pray tell, is an "isolator"?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Pud]

Hi all,

V = 415, 3Ph, N + E. 50Hz.
Load max is during injection phase (hydraulics), so rated figureis peak A.
An isolator is a wall mounted switch (near machine) which can isolate machine from the supply. No idea if it's regs but seems common practise over here.

Thanks guys/gals

www.tynevalleyplastics.co.uk

Politicians like to panic, they need activity. It is their substitute for achievement.

 

[ScottyUK]

Keith,

Isolator: usually a fault-making, load breaking switch capable of achieving a minimum contact separation in the open state and being secured with a padlock. This type of thing.

 

[waross]

Oh, a disconnect switch or a fused disconnect. Got it.
Thanks.

Something to consider if you find a 45 KVA machine in a position where only 43.6 KVA is available;
Generally it takes a lot more BTUs, kWs, energy, (whatever you want to call it) to bring a product up to temperature than to hold it at working temperature.
Starting your injection motor may be even more problematic than running up to 45 KVA.
Consider having the controls modified so that the heating load is dropped off for about 10 seconds while the motor is started.
Don't start the injection motor until the product is up to temperature.
Once the motor is running, curtail the heating enough to allow the machine to run at less than about 90% x 45 KVA or 40.5 KVA.
Scotty calculated the KVA based on 400 Volts. At 415 Volts, 63 Amps will get you 45.28 KVA.
BUT BEWARE: If your machine is rated for 45 KVA at 400 Volts it will probably take more than 45 KVA at 415 Volts.
When the numbers are this close to 100% you may consider having someone competent look at and evaluate the installations.
There may be some important "It Depends" issues.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Thanks for the "isolator' responses.

Hi Bill. I was just wiring a new CNC mill and the name plate said 42A @ 230V. I told the customer you only have 20A run to the location but he insisted that would be far more than needed. He then dragged me over to three other machines that he told me were currently working on the highest load parts they ever make. I whipped out my clamp-on and sure enough, 4.2A, 4.7A and 5.1A. I mention this only because depending on lots of things machines can often use far less than the maximum nameplate current -forever-. Spending a lot of money to match the nameplate can often waste a lot of money. It might behoove one like the OP, with someone competent helping, to do a quick temporary hook up with what's available then actually check the loading.

That other customer I have that's wrestling with the morons at the local power company as he's trying to get the power needed to match his mill's name plate power; 100A @ 230V, 3ph. I keep telling him "use what you have until you see what you really need". I've explained that since he's not even a production shop all he needs to do is hog a bit slower and he can make a huge difference in his requirements. Economically it will be a large improvement on his expenses to cut a little slower once in a while instead of paying the service's ready-to-service serve costs just so once every 3 years he can hog something in 10 minutes instead of 20. He won't listen. It's costing him many tens of thousands of dollars on this quest.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Running a 20 Amp feeder to a machine rated at 42 Amps. Sure it may work forever in the real world, But- don't pull a permit or let an inspector see it.
It is a matter of code compliance, not actual current.
However, the good news is that you can use the low currents to justify a high diversity factor or low demand factor on upstream feeders.



Bill
--------------------
"Why not the best?"
Jimmy Carter