9inch grinder on domestic power supply

[phatboy]

Hi,

I've read a few places that 9inch grinders being around 2000w @ 230v often trip standard domestic power supplies on startup. Is there any truth in this?

I will be buying a machine soon, and a soft start one is tempting for a couple of reasons, but they seem to be a lot more expensive when in a carry case?!

Any advice or recommended tools appreciated!

Tim

 

[PrenticeBoyofDerry]

It is likely the start up inrush current can overload the circuit breaker, you could swap out the breaker likely a b type, for c type, providing the earth loop impedance of the circuit comply. This helps deal with the short period that the start up/inrush current is present.

 

[DaveHerns]

My B&Q 9" grinder was OK on a 10m extension lead fused at 13 amp. Think it has soft start , only used it for one afternoon

 

[Belle427]

Ive used mine quite a lot on a B32 protected ring main and it has never tripped. No soft start feature and its a 2100 watt Hitachi grinder.

 

[bernardgreen]

Does it dip your lights when it starts ? more important does it affect your neighbours lights ?

 

[DaveHerns]

I only use my angle grinder, pressure washer, air compressor , arc and mig welders in daylight hours so my neighbours wouldn't know if their lights would dim!

 

[phatboy]

It is likely the start up inrush current can overload the circuit breaker, you could swap out the breaker likely a b type, for c type, providing the earth loop impedance of the circuit comply. This helps deal with the short period that the start up/inrush current is present.

It would only be for the occasional indoor job whilst we renovate, so I'd not want to change out the breaker. The garage however is wired with a C curve breaker so may be able to run a loooong lead from there.

I have a dedicated socket on a B16 in the house, I suppose is more likely trip than a lightly loaded B32 ring?!

Thanks
Tim

 

[^woody^]

No chance of a cuppa in your house then with a 2kW kettle

 

[phatboy]

No chance of a cuppa in your house then with a 2kW kettle

Do kettles have a large inrush current, like a motor might?!

 

[muggles]

My 2400w Bosch hasn't ever tripped a power supply, does have soft start though... no idea what the inrush current of a kettle is compared to a motor, but my kettle is 3kW and that's fine, so is my 3.1kW iron

 

[bernardgreen]

Do kettles have a large inrush current, like a motor might?!

No The heating element in a kettle is resistive and has a practically constant resistance ( it varies slightly at the temperature in the element increases ).

A motor has a vey low resistance and therefore will take a lot of current when stationary. But when the motor is rotating it generates a back EMF in the windings. This is a voltage in the opposite direction to the applied supply voltage. This back EMF creates a current in windings but in the opposite direction to the supply current so the resultant current in the windings is much lower than it was when the motor was not rotating.

 

[^woody^]

Do kettles have a large inrush current, like a motor might?!

No The heating element in a kettle is resistive and has a practically constant resistance ( it varies slightly at the temperature in the element increases ).

A motor has a vey low resistance and therefore will take a lot of current when stationary. But when the motor is rotating it generates a back EMF in the windings. This is a voltage in the opposite direction to the applied supply voltage. This back EMF creates a current in windings but in the opposite direction to the supply current so the resultant current in the windings is much lower than it was when the motor was not rotating.

In English please.

Surely a kettle goes from a state of no draw to maximum draw when switched on just like a grinder that does not have soft start?

 

[bernardgreen]

Surely a kettle goes from a state of no draw to maximum draw when switched on just like a grinder that does not have soft start

Yes the kettle does that, the resistance of it's element doesn't change, it is a resistive load.

The angle grinder and almost every other motor appears to change the "resistance" of its windings to current flow from a very low "resistance" at stand still to a higher "resistance" when the motor is rotating. The actual resistance of the windings does not change but the rotation generates a voltage in the windings that opposes the supply voltage so that the voltage driving current through the resistance of the windings is lower and hence less current flows through the windings.

 

[^woody^]

But a kettle of 2kw at 230v is going to draw the same current as a 2kw grinder at 230v. So any MCB won't know the difference and would trip regardless once the threshold for the MCB is exceeded?

 

[foxhole]

I find the cheaper machines are problematic, have a cheap chop saw which will trip my garage supply every time, have to use it from the house ring main or it trips.