**** Pump and MCBs!

[bernardgreen]

Missed this bit out

If the tank has been filling up with solid material while the pump was out of action then the macerator is likely to have much thicker sludge to "chew" and hence the time taken for the motor to reach speed is longer than normal. This would mean the period of start up current would be longer and thus long enough to trip the thermal trip in the MCB

 

[JohnW2]

If the tank has been filling up with solid material while the pump was out of action then the macerator is likely to have much thicker sludge to "chew" and hence the time taken for the motor to reach speed is longer than normal. This would mean the period of start up current would be longer and thus long enough to trip the thermal trip in the MCB

That is certainly a theoretical possibility. However, I would have doubted that the start-up time would, even in the scenario you describe, be long enough to thermally-trip an MCB and, if it were, it might well also thermally damage the motor.

Kind Regards, John

 

[securespark]

Are you assuming that it is buried SWA? Whatever, I don't think the CCC needs to be high enough for the very brief start-up current. It's whether the MCB trips, and if the Zs is low enough (if a Type C MCB were used) that actually matter, isn't it?

By brief, what do you mean? The current will decay, of course, but it could last 3/4 seconds.

Sometimes type D's can be used on motor circuits (obviously Zs allowing). Yes, they matter. I didn't say they weren't important.

Yes, I did assume. Shoot me! But the OP could confirm the installation method.

So the MCB could be upped to 20/25A and type changed dependent on Zs.

 

[securespark]

Need a picture of the CU.

It could be an older model with Type 1/ Type 2 MCB's.

 

[333rocky333]

1995 mk I think were the same profile at the time as Merlin gerin, as in the right hand photo
Not ideal but as the new schneider ones still fit the old Merlin gerin, then its likely the new schneider will also fit your board

They then changed to the ones in the left picture and have changed again since then i think

 

[Iggifer]

When did MK phase out the 3871s? I know the standard was withdrawn in 94 but if they didn't predate that by much it's possible that he's got 3871s

 

[charliegolf]

I have the LN59xx series of mcbs. (On the right) All 'B' models. It's being suggested to use 'c' if I can, 'cos they're motor rated?

 

[JohnW2]

By brief, what do you mean? The current will decay, of course, but it could last 3/4 seconds.

Agreed.

Up to 5 seconds or so, one can assume adiabatic conditions. Per the usual adiabatic calculation, a 2.5mm² copper conductor is allowed to carry about 160A for those 5 seconds. I would suggest that it is that which matters, not the 'continuous current CCC' of the cable (be that 29A or whatever).

Kind Regards, John

 

[Simon35]

I'm not sure that I understand your arithmetic - by my reckoning, 1.5kW at 240V is about 6.25A.

In any event, I imagine that what is being quoted is probably the running current, whereas the OP's problem is related to the start-up current (which could be several times greater than the running current).

Kind Regards, John

I didn't need to do any arithmetic. I just looked at the motor current table in a folder on my desk at work. Manufacturers information confirms 13.6A at 230V.

 

[securespark]

I Manufacturers information confirms 13.6A at 230V.

Confirms 13.6A as what?

FLC or start-up?

 

[JohnW2]

I didn't need to do any arithmetic. I just looked at the motor current table in a folder on my desk at work. Manufacturers information confirms 13.6A at 230V.

Whatever the manufacturer might say, I still don't understand (or agree with) the statement of yours on which I was commenting ....

Google sez 1.5kW.....so 12A at 240V

That statement certainly implies (incorrect) arithmetic. Also, it refers to Google as the source, not 'the folder on your desk'.

Kind Regards, John

 

[Adam_151]

I have the LN59xx series of mcbs. (On the right) All 'B' models. It's being suggested to use 'c' if I can, 'cos they're motor rated?

Those in the RHS picture posted by rocky are rebadged Merlin Gerin/schneider C60 multi-9 breakers, while mix and match isn't desireable, when its just a case of badge engineering going on, its not the biggest sin in the book. Unfortunatly the C60 range is no longer current and has been replaced with IC60 (acti-9) [they state these as being compatable with the older ranges, but often look out of place]

The good news if you should be able to track down a multi-9 breaker in suitable rating, becuase there must have been hundreds of thousands fitted over the past twenty years, mostly in commericial and industrial environments, so C types of most ratings will be obtainable

https://www.ebay.co.uk/sch/i.html?_...0.Xmulti+9+c16.TRS0&_nkw=multi+9+c16&_sacat=0

 

[Simon35]

Whatever the manufacturer might say, I still don't understand (or agree with) the statement of yours on which I was commenting ....
That statement certainly implies (incorrect) arithmetic. Also, it refers to Google as the source, not 'the folder on your desk'.

Kind Regards, John

It implies nothing of the sort. I googled the pump type supplied by the OP, discovered it was 1.5kW, and then found the flc of a single phase 1.5kW motor from some information I had. What I didn’t do was some incorrect calc and then proceed to determine cable sizes and breaker ratings from that calc.

It only implies incorrect arithmetic because you assume your method of calculation is correct, when in fact it's not.

Confirms 13.6A as what?

FLC or start-up?

FLC. When a motor manufacturer quotes tje motor current, they provide the flc, not the start-up current.

 

[JohnW2]

It implies nothing of the sort. I googled the pump type supplied by the OP, discovered it was 1.5kW, and then found the flc of a single phase 1.5kW motor from some information I had. What I didn’t do was some incorrect calc ...

OK, fair enough - but that was definitely not how I (or EFLI interpreted:

Google sez 1.5kW.....so 12A at 240V

... which looks as if it is just a 'calculation'.

It only implies incorrect arithmetic because you assume your method of calculation is correct, when in fact it's not.

I have conceded that 'my' (and EFLI's) calculation assumed a PF of 1.0. If the PF is about 0.52, then 1.5kW would, indeed, be about 12A at 240V.

However, something else confuses me. In the statement we are discussing, you referred to "12A at 240V", and are now saying that that derives from the manufacturer's information. More recently, you have been saying that the manufacturer states "13.6A at 230V". Which is correct in terms of the manufacturer's information?

Kind Regards, John

 

[Simon35]

OK, fair enough - but that was definitely not how I (or EFLI interpreted:

... which looks as if it is just a 'calculation'.
I have conceded that 'my' (and EFLI's) calculation assumed a PF of 1.0. If the PF is about 0.52, then 1.5kW would, indeed, be about 12A at 240V.

However, something else confuses me. In the statement we are discussing, you referred to "12A at 240V", and are now saying that that derives from the manufacturer's information. More recently, you have been saying that the manufacturer states "13.6A at 230V". Which is correct in terms of the manufacturer's information?

Kind Regards, John

From the MI, the product of efficiency and power factor is 0.49. At 240V, that gives 13A in fact, so my figure was a bit low, but in the right area.