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How do you size the MCB, wire and protection for a motor in the UK/Europe? How is it typically done?

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If anyone is curious here how its done in the US:


You size the conductor based on 125% of tables 430.247-430.250 determined by the type of motor and duty cycle of course. (When Table 430.249 says 2 phase they don't mean 180* out of phase like in 120/240 but 90* out of phase- this was common 100 years ago during the electrification of the United States but obsolete today)

This will then take you to table 310.15 B 16:


60*C or 75*C based on your wire and termination. Typically you use 75*C, and de-rate (more than 3 conductors in a conduit) off the 90*C column as THHN/THWN is rated 90*C. Once the conductor size is known you size the fuse/breaker based on Table 430.52.

For a breaker you can size at 250% of the conductor's ampacity (current carrying capacity), for a none time delay fuse 300% and for a time delay fuse 175%.

Remember there is no loop impedance requirement- meaning you can place #14 (2.08mm2) on a 40 amp breaker and run it as long as you like, ie 500 feet or more.

Next, you size the motor's overload protection based off 115% to 125% of the motor's actual nameplate rating.

If any of you have 3 hours time to burn, here is a crash course on the subject;

Over all idea under the NEC:

View: https://www.youtube.com/watch?v=_7FmwY442dQ



Sizing the breaker/fuse (Short circuit and ground fault protection of the wires):

View: https://www.youtube.com/watch?v=nvJaaWGJMo0



Sizing the conductors:

View: https://www.youtube.com/watch?v=Sic1uoua3og



Sizing of the overload protection for the motor and wires:


View: https://www.youtube.com/watch?v=2cprO8ZdT1U
 

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  • Thread Starter Thread Starter
  • #3
What about pumps, an air handling unit, AC unit, elevator motor, industrial motor? How do you size the circuit? What about a stand alone motors?
 

Megawatt

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Arms
Advent Win
What about pumps, an air handling unit, AC unit, elevator motor, industrial motor? How do you size the circuit? What about a stand alone motors?
How do you size the MCB, wire and protection for a motor in the UK/Europe? How is it
.............................................................................................................


If anyone is curious here how its done in the US:


You size the conductor based on 125% of tables 430.247-430.250 determined by the type of motor and duty cycle of course. (When Table 430.249 says 2 phase they don't mean 180* out of phase like in 120/240 but 90* out of phase- this was common 100 years ago during the electrification of the United States but obsolete today)

This will then take you to table 310.15 B 16:


60*C or 75*C based on your wire and termination. Typically you use 75*C, and de-rate (more than 3 conductors in a conduit) off the 90*C column as THHN/THWN is rated 90*C. Once the conductor size is known you size the fuse/breaker based on Table 430.52.

For a breaker you can size at 250% of the conductor's ampacity (current carrying capacity), for a none time delay fuse 300% and for a time delay fuse 175%.

Remember there is no loop impedance requirement- meaning you can place #14 (2.08mm2) on a 40 amp breaker and run it as long as you like, ie 500 feet or more.

Next, you size the motor's overload protection based off 115% to 125% of the motor's actual nameplate rating.

If any of you have 3 hours time to burn, here is a crash course on the subject;

Over all idea under the NEC:

View: https://www.youtube.com/watch?v=_7FmwY442dQ



Sizing the breaker/fuse (Short circuit and ground fault protection of the wires):

View: https://www.youtube.com/watch?v=nvJaaWGJMo0



Sizing the conductors:

View: https://www.youtube.com/watch?v=Sic1uoua3og



Sizing of the overload protection for the motor and wires:


View: https://www.youtube.com/watch?v=2cprO8ZdT1U
Cookie these guys don’t want to see Mike Holts videos because it doesn’t apply to them and if you took the masters test you would probably fail. First off you don’t add 125% unless it’s a continuous duty motor, there is no such thing as 2 phase in our trade it’s called single phase. The only thing on the nameplate of the motor is the service factor and HP. the NEC decides how many amps it will pull not the nameplate rating on the motor. If you don’t use the service factor how do you size your overloads. Deration factors don’t apply except in hot areas like on roofs. As far as current carrying conductors after 4 wires the ampacity of the wires drops to 80%
 
  • Thread Starter Thread Starter
  • #6
There was very much 2 phase power 90* out of phase, hence why the code specifically gives a table "single phase" and a table "two phase"



The thing is in the IEC world split phase (180* out of phase 120/240) is routinely called "2 phase" but its not the same 2 phase as when North East America was first energized.


The motors used in Commercial applications like pumps, fans, ect would certainly be classified as continuous and the rules in 430.22 would certainly apply.


The motor nameplate lists the amps:



1575397620416.png



1575397654542.png


Those amps are used to size the protection overload heaters, not the wire itself. 115 to 125% of the nameplate amps as based on the service factor.

Yes- at more than 3 wires you start to derate the values in table 310.15 B 16. Technically 4 wires as the neutral in a multi wire branch circuit (MWBC) does not count as a current carry conductor in the eyes of the code.

Lastly, see my snap shot. The code table is for the breaker and wire size, name plate is for the overloads.
 

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Megawatt

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Arms
Advent Win
There was very much 2 phase power 90* out of phase, hence why the code specifically gives a table "single phase" and a table "two phase"



The thing is in the IEC world split phase (180* out of phase 120/240) is routinely called "2 phase" but its not the same 2 phase as when North East America was first energized.


The motors used in Commercial applications like pumps, fans, ect would certainly be classified as continuous and the rules in 430.22 would certainly apply.


The motor nameplate lists the amps:



View attachment 54297



View attachment 54298


Those amps are used to size the protection overload heaters, not the wire itself. 115 to 125% of the nameplate amps as based on the service factor.

Yes- at more than 3 wires you start to derate the values in table 310.15 B 16. Technically 4 wires as the neutral in a multi wire branch circuit (MWBC) does not count as a current carry conductor in the eyes of the code.
Cookie why are we talking about phase arrangements and no you do not go by the FLC on the motor you go to article 430 look up you HP then you are doing it by code. Do you know the meaning of continuous duty but since you are quoting the code book I will tell you. It means motors, lights etc. that runs 3 hours or more
 
  • Thread Starter Thread Starter
  • #8
I merely explained that when 430.249 says "Two phase 4 wire" they are not talking about split phase 120/240.

As I said- you use 430.22 to size the wire, and 430.32A to size the motor's protection. 430.32A says to use the nameplate. Let me find it and I will post it.
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Here is 430.32A, which specifically mentions using the name plate to size the overloads.

Like I said, pumps, fans, ect are continuous duty applications. Aas an example a hydronic recirculating pump will run 24/7 when the outside building temp is below 55*F.
 

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Megawatt

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Arms
Advent Win
I merely explained that when 430.249 says "Two phase 4 wire" they are not talking about split phase 120/240.

As I said- you use 430.22 to size the wire, and 430.32A to size the motor's protection. 430.32A says to use the nameplate. Let me find it and I will post it.
Post automatically merged:

Here is 430.32A, which specifically mentions using the name plate to size the overloads.

Like I said, pumps, fans, ect are continuous duty applications. Aas an example a hydronic recirculating pump will run 24/7 when the outside building temp is below 55*F.
Cookie I passed the masters test, who are you trying to teach. I don’t need Mike Holts information I already know it i have wired , sized , installed 3 phase motors for 33 years. I guess Mike Holt is wrong you use the current the code book gives you not the nameplate. You have a lot to learn. Quit quoting the code book to me on stuff I already know
Post automatically merged:

Cookie I passed the masters test, who are you trying to teach. I don’t need Mike Holts information I already know it i have wired , sized , installed 3 phase motors for 33 years. I guess Mike Holt is wrong you use the current the code book gives you not the nameplate. You have a lot to learn. Quit quoting the code book to me on stuff I already know
Cookie you are just reading a book, I’m telling you with out a book, I already know the code that’s why I’m a master and your not
Post automatically merged:

Cookie I passed the masters test, who are you trying to teach. I don’t need Mike Holts information I already know it i have wired , sized , installed 3 phase motors for 33 years. I guess Mike Holt is wrong you use the current the code book gives you not the nameplate. You have a lot to learn. Quit quoting the code book to me on stuff I already know
Post automatically merged:


Cookie you are just reading a book, I’m telling you with out a book, I already know the code that’s why I’m a master and your not
This topic is over it’s a UK forum so quit boring everybody
 
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davesparks

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Mentor
Arms
Esteemed
Cookie why are we talking about phase arrangements and no you do not go by the FLC on the motor you go to article 430 look up you HP then you are doing it by code. Do you know the meaning of continuous duty but since you are quoting the code book I will tell you. It means motors, lights etc. that runs 3 hours or more
He's talking about phase arrangement because it's interesting, 90 degree 2 phase is not something we've ever had here and it is always nice to learn something.

I find it quite odd that you would look up a current rating in the book based on HP rather than using the FLC of a motor.
But I guess things are done differently where you are, we come across motors of different efficiency ratings and so the conversion from HP to Amps is not the same for every motor.

As a general rule for us we use manufacturers data wherever it is available and a book value if no more specific information is available. This goes for a variety of different things, not just motors.
 

Megawatt

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Arms
Advent Win
Cookie I passed the masters test, who are you trying to teach. I don’t need Mike Holts information I already know it i have wired , sized , installed 3 phase motors for 33 years. I guess Mike Holt is wrong you use the current the code book gives you not the nameplate. You have a lot to learn. Quit quoting the code book to me on stuff I already know
Post automatically merged:


Cookie you are just reading a book, I’m telling you with out a book, I already know the code that’s why I’m a master and your not
Post automatically merged:


This topic is over it’s a UK forum so quit boring everybody
Since you are in article 430 let’s say you have a 20 hp 3 phase 6 lead continuous duty motor what size wire does it require and what size maintenance disconnect does it take
Post automatically merged:

Nobody said they did, the OP has asked how we size the cables.
Nobody cares how you size cables
 
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  • Thread Starter Thread Starter
  • #13
Cookie I passed the masters test, who are you trying to teach. I don’t need Mike Holts information I already know it i have wired , sized , installed 3 phase motors for 33 years. I guess Mike Holt is wrong you use the current the code book gives you not the nameplate. You have a lot to learn. Quit quoting the code book to me on stuff I already know
Post automatically merged:


Cookie you are just reading a book, I’m telling you with out a book, I already know the code that’s why I’m a master and your not
Post automatically merged:


This topic is over it’s a UK forum so quit boring everybody
You are correct in terms of sizing wire- you use the code. In terms of setting overload protection you use the nameplate on the motor. I doubt Mike Holt is wrong, certainly not on something so basic.


I'm quoting code because on black and white it vindicates my assertions.


I'm curious to hear from the UK guys on how they would do a motor install. Especially with type B, C, and D MCBs to choose from.
 
  • Thread Starter Thread Starter
  • #14
Since you are in article 430 let’s say you have a 20 hp 3 phase 6 lead continuous duty motor what size wire does it require and what size maintenance disconnect does it take
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Nobody cares how you size cables

125% of 54 amps (230 volts) = 67.5 amps

125% of 27amps (460 volts)= 33.75 amps

Assuming 3 wires in conduit and 75*C terminations we get:

#4 (21.15mm2) copper at 230 volts

#10 (5.26mm2) copper at 460 volts


For 60*C terminals:

#4 (21.15mm2) copper at 230 volts

#8 (8.37mm2) copper at 460 volts

I'd put the 230 volt unit on 100amp disco and the 460 volt unit on a 60amp disco as 30, 60 and 100 are standard sizes.
 

ElectroChem

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Arms
For a single motor supply circuit here in Australia I would size the overload protection to the FLC from the motor nameplate. (There are a couple of regs around which motors do and don't need overload protection).
Then the circuit protection would be the next size up from there i.e. a 7.6A FLC motor would need at least a 10A supply, possibly with a D-curve breaker if it's a heavy starter.
Cable would then be sized to the supply based on the standard tables in AS3008 or calculated from scratch (rarely). Rules of thumb are also common like using 2.5mm for smaller circuits in industrial settings.
 

Lucien Nunes

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Mentor
Arms
Esteemed
90 degree 2 phase is not something we've ever had here and it is always nice to learn something.
I think we have used it here historically in a couple of supply systems, I would have to look it up. IIRC there were two implementations, one used equal sized supplies and symmetrical motors, the other used a lower-rated 'teaser' phase with 1-ph load always on the main phase.

I always cringe when people call a circuit using two line conductors from a 3-phase supply '2-phase' as it's often more trouble than it's worth to explain why it isn't!
 

Lucien Nunes

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Mentor
Arms
Esteemed
I find it quite odd that you would look up a current rating in the book based on HP rather than using the FLC of a motor.
I believe the logic, and perhaps Cookie can comment, is that the circuit (which is not adjustable after installation) should be sized to allow sufficient ampacity for any standards-compliant motor of that power that might be fitted now or in the future, that might have a marginally different FLC compared to the one specced at installation time. But the overloads are set according to the particular motor in use, based on nameplate FLC.
 
  • Thread Starter Thread Starter
  • #18
I believe the logic, and perhaps Cookie can comment, is that the circuit (which is not adjustable after installation) should be sized to allow sufficient ampacity for any standards-compliant motor of that power that might be fitted now or in the future, that might have a marginally different FLC compared to the one specced at installation time. But the overloads are set according to the particular motor in use, based on nameplate FLC.

You got! :)

The code mandates larger wire in the event the new motor coming in has a higher FLC. Also, HVAC techs, electricians and maintenance guys are always told to re-adjust the motor overloads when replacing an old motor with a new one. Its common to forget.
 
  • Thread Starter Thread Starter
  • #19
I think we have used it here historically in a couple of supply systems, I would have to look it up. IIRC there were two implementations, one used equal sized supplies and symmetrical motors, the other used a lower-rated 'teaser' phase with 1-ph load always on the main phase.

I always cringe when people call a circuit using two line conductors from a 3-phase supply '2-phase' as it's often more trouble than it's worth to explain why it isn't!


If you look at old power lines that are still in service in US cities you can even see the remnants of 2 phase power. Often the cable riser pot will have 4 bushings and a 4th insulator (without a conductor in it) on the cross arm or the cross arm with have insulator pins in multiples of 4 instead of 3. The 2 phase was abandoned and changed to 3 phase decades ago but the old stuff remains.



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Here is a pic I took of one of those poles 10 years ago:
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Only the pic to the right is mine, the one on the left is AR's from Ipernity.
 

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