Maximum size for a UK Direct Online Motor starter

Good afternoon,

Is there any practical legislation governing the starting methodology for motor operation in the UK for three phase motors?

I've seen various recommendations or best practice for applying soft starting methodology for motors over certain sizes but I can't find any solid reasoning or evidence for such requirements.

For instance, I've got a 22kW motor and by "best practice" methodology I would generally use a method of soft starting to operate the motor such as Star/Delta or Electronic Soft Start to reduce the inrush where I don't necessarily require speed control.

However a 7.5kW motor I would generally install on DOL unless it requires speed control.

I've come across a customers specification stating that any motor above 5.5kW should use soft starting methodology. I'd like to challenge this as its an expensive solution for a panel full of star/delta starters vs DOL.

The motors are generally operating pumps.

Any guidance would be appreciated.

Parents
  • In terms of specified / quantified limits and rules, I believe I'm right in saying that the limiting factor will be voltage dips on the supply and the effect that has on other (possibly future) customers*.To that end DNO's will require conformity to EREC P28/2. It is not a particularly user-friendly document, but it does quantitively address things like inrush magnitude, frequency of operation and supply impedance.

    (*What happens in the customer's own network is their own shout, and what is acceptable will of course depend on the nature of their loads)

    There are varying levels of detail required, which can be as little as a statement from the manufacturer to the effect that equipment conforms BS EN 61000-3-3 or BS EN 61000-3-11 and flicker isn't an issue with supplies of at most XYZ impedance (which you can then ascertain by testing), or as much as detailed network modelling, with levels of detail in between.

    It is a requirement of the Distribution Code and hence implicit in supply agreements, and it is what DNOs refer to (in theory) when assessing, say, heat pumps or other disturbing loads when consent is requested to connect them. Certainly it is the stick that'll be used to beat you if there are complaints.

Reply
  • In terms of specified / quantified limits and rules, I believe I'm right in saying that the limiting factor will be voltage dips on the supply and the effect that has on other (possibly future) customers*.To that end DNO's will require conformity to EREC P28/2. It is not a particularly user-friendly document, but it does quantitively address things like inrush magnitude, frequency of operation and supply impedance.

    (*What happens in the customer's own network is their own shout, and what is acceptable will of course depend on the nature of their loads)

    There are varying levels of detail required, which can be as little as a statement from the manufacturer to the effect that equipment conforms BS EN 61000-3-3 or BS EN 61000-3-11 and flicker isn't an issue with supplies of at most XYZ impedance (which you can then ascertain by testing), or as much as detailed network modelling, with levels of detail in between.

    It is a requirement of the Distribution Code and hence implicit in supply agreements, and it is what DNOs refer to (in theory) when assessing, say, heat pumps or other disturbing loads when consent is requested to connect them. Certainly it is the stick that'll be used to beat you if there are complaints.

Children
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