Please explain this motor plate

[R.thompson]

Please could someone explain to me about this motor plate for a pump and why the numbers don't seem to add up, such as why the amps don't correlate with the watts when connected to the nominal voltage. Also what kind and type of protection is needed for the pump. Many thanks.

 

[Darkwood]

Hi welcome to the forum, The Kw rating on the plate is not an Electrical value its a mechanical value namely the turning energy available at the shaft, do not convert this direct to electrical power without the correct calculation or you will be scratching your head.

 

[Lucien Nunes]

P1= input power. P2= output power.
Input VA = V.I = 230 x 4.9 = 1127VA
Power factor = P1/ input VA = 1050/1127 = 0.93
Efficiency= P2/P1 = 780/1050 = 0.74

As this is a 1hp motor it should be equipped with thermal overload protection, and if hazard could arise from unexpected restarting, zero-volt release.

 

[Deleted member 26818]

I is another denominator for A (Amps).

 

[davesparks]

I is another denominator for A (Amps).

Eh what?

 

[Lucien Nunes]

Well, sort-of. 'I' is the symbol for the quantity 'current' which we measure in units of 'amps', for which the symbol is 'A'. Although it's not laid out well, it does say I 4.9 A.

 

[Marvo]

They've made life very easy with the info on this particular plate, P2 is the power output (mechanical power) and P1 is the power input (electrical power). 'I' is the absolute maximum permitted run current.

 

[telectrix]

P1= input power. P2= output power.
Input VA = V.I = 230 x 4.9 = 1127VA
Power factor = P1/ input VA = 1050/1127 = 0.93
Efficiency= P2/P1 = 780/1050 = 0.74

As this is a 1hp motor it should be equipped with thermal overload protection, and if hazard could arise from unexpected restarting, zero-volt release.

what are the H values?

 

[UKMeterman]

I suspect the H value is the HEAD of water (pressure) in meters it can achieve at a given flow rate is 10 and the maximum pressure it can achieve is 17m

 

[Lucien Nunes]

Indeed. The flow rate is 16 cubic metres per hour at a pressure of 10 m.c.a. (metros columna de agua). Power delivered into the water is Q.H.rho.g/3600 = 16x10.1000.9.81/3600 = 436W. Efficiency of the pump itself at 10m head is 436/780 = 0.56.

 

[Marvo]

Yep H is head pressure and m.c.a. is a unit of pressure (meters column of water). 1m.c.a = 0.98 Bar. 1m.c.a = 1.42 PSI. They give the Q=Flow rate that the pump will achieve at 10 meters of head at sea level.

They also give the max head pressure the pump should be run at as being 17 meters and often with a centrifugal or multistage centrifugal pump there's a minimum head pressure requirement as well. Sometimes the minimum head requirement is to prevent electrical overload and sometimes it's to prevent mechanical issues such as impellor lift and cavitation.

 

[R.thompson]

Oh wow!! Thanks guys! Wasn't expecting such an excellent response in so little time. You have enlightened me so much.

Taking into account everything that has been said, am I right in thinking that the protection that the pump has is incorrect? (note that I didn't design this installation so am not familiar with its specific needs and circumstances.) See image attached.

The 10A breaker to one side, because it protects the lighting, the C40A is the wrong type and should be of a lower rating and be double pole protection instead of single. Maybe something like a double D10A breaker would be a better choice. Whats more, a RCD with a rating of 0.003A, seeing as this is for an outdoor swimming pool, would improve the safety for the users. From my point of view, the motor starter and thermal protection is also inadequate and should be a max of 5A instead of 6.3-10A

 

[Marvo]

The pump motor may have an internal thermistor protection that can be wired back to a relay or DOL starter, this is the best type of protection and most likely to detect issues before damage occurs. If not, the type of manual motor starter you have in the photo would be fine to provide adequate pump protection except it requires a lower current range so it'll have to be replaced.

The circuit breakers (MCB's) protect the installation wiring, not the pump itself, so they should be sized according to the wiring sizes and C or D curve are okay if they can meet disconnect time requirements on that particular circuit. If this is a pool pump then an RCD would be appropriate for the pump but I doubt you'll find a 3mA RCD, a 30mA would be considerably cheaper and fine. The lighting should be fed from an isolating transformer so an RCD shouldn't be necessary for the lights.

 

[Lucien Nunes]

The C40 MCB rating seems a bit random, perhaps someone didn't have the right rating and just put it there as an isolator, knowing that the circuit was adequately protected upstream? I'm not sure why you want a DP breaker specifically. There's no harm in it but an SPSN breaker like that (of more suitable rating) should be fine on a single-phase circuit. DP breakers will respond to overcurrent and faults in both poles but with an earthed neutral it's almost impossible for a situation to arise where it would respond to such a current in its neutral pole that doesn't also pass through the line.

BTW is this in the UK or Spain?