Curious Power Issue while using Chain Saw with Extension Cable!

Section62

ThisIsWeird said:

16A is low for 'sockets', unless it supplies a very limited number, say upstairs bedrooms. I mean, a couple of heaters used during winter would trip that MCB if used at the same time.

16A wouldn't be a bad choice for a radial circuit wired with 2.5mmsq (if that's what it is).

Also bear in mind this is a shed/garage(?) with a supply running possibly tens of meters from the main consumer unit, using goodness knows what type of cable to get there.  I'd be happy to bet this was scrimped on a bit, so could just be 2.5mm SWA.  The installer may have taken the view that since the feed to the shed/garage had limited capacity there was no point/was a sensible precaution to fit the shed/garage CU socket circuit with a 16A MCB.... just in case the user decided to plug in multiple heaters and then try to run a powerful chainsaw, all at the same time.  (if it were me, I'd always prefer the 'sockets' MCB to trip first, not the one on the main CU, so I don't get plunged into darkness with a still rotating power tool in my hands.  AKA "discrimination")

It also wouldn't surprise me if the 20A MCB's are doing nothing more than filling the spare ways on the CU.

ThisIsWeird said:

Have to say, I thought S62's remark re added resistance potentially leading to increased current draw was weird, but I get what he says - a high-draw device with a large initial surge, coupled with being laboured by a voltage drop, is a good theory - just enough to send the MCB over the top when the trigger is pulled. It wouldn't take much for a 16A MCB to trip - it's not actually a fault as such, just a too-low rated or too-fast an MCB. But, it's the one for that circuit, so shouldn't be interfered with other than by a pro. 
So, what do the 20A jobbies supply?

Totally agree with the BiB in this case.

ThisIsWeird

Ah. That that whole CU is in the garage? 
Oops.

sujsuj

Section62 said:

grumbler said:

Section62 said:

grumbler said:

Section62 said:

sujsuj said:

I was trying to cut some wood using my RYOBI 2300W 40cm Chainsaw (RCS2340B). I used extension cables 13A rated its 25 meter long. But when I connect Chainsaw at end of extension cable power trips and Chainsaw stopped working. I could connect Chainsaw directly to plug and it works.

If it is the MCB tripping then there's a good chance the issue is the volt drop over 50m of low-cost extension cable is resulting in a current draw high enough to cause the MCB to trip.  What rating is the MCB, if it is that which is tripping?  (a photo may be best)

This makes no sense. Higher cable resistance (and, as a result, higher voltage drop over the cable) can result only in lower current, that cannot cause MCB tripping.

Were you basing that on I = V / R  ....or something else?

Whatever. You cannot increase the current by adding an extra resistor in sequence, can you?

Quite important to understanding sujsuj's problem.

He has a largish inductive load in an AC circuit, with the additional complication of it being a motor driving a mechanism with (probably*) a fair degree of mechanical resistance.

I've not delved into the detail of this model's design, but it is a reasonable assumption that at the moment of switch-on there will be a 'locked rotor' scenario. The peak current drawn by the motor (and its duration) has more to do with the design of motor, loading, and the amount of power required to get the motor up to speed, less to do with the resistance of the cable.  Also bear in mind the cable is technically capable of carring a far greater current than 13A @230V, but is rated at 13A (or whatever) for safety and longevity.  Pure electrical resistance isn't the determining factor here - the power requirement to get the motor spinning at operational speed is.  Making the motor suffer an excessive voltage drop will make it need to work harder for longer to achieve the stable state.  And more current for longer is what can make an MCB trip.

I've had the same scenario as FreeBear and used the same solution... but that isn't one that sujsuj should contemplate.  If the chainsaw works in the wall socket, but not on the end of 50m of flex, then the problem is with the flex, not the supply.

Don't believe me?  The manual for sujsuj's chainsaw (unusually) goes as far as stating you should "Connect the product to a power supply with an impedance equal to or less than 0.33 Ω to minimise voltage fluctuations." although it doesn't explain how the user should find the impedance of their power supply, other than the less than helpful "Contact your electric power supplier for further clarification".  Suffice to say that connecting it to the end of 50m+ of not very suitable flex is unlikely to help.

(*I'd wonder whether the chain has been correctly re-tensioned and lubricated recently)

Just to be clear I placed chain in the chainsaw  on the day I posted this tread only. It was RIOBI's first use. I connected directly to the socket and cut wood piece to ensure all good before trying out at the end of these two extension cables. I made sure lubricant is there in chain as well. I reduced tension and tried gain when the power tripped first to ensure I am not putting too much tension. Thanks

sujsuj

grumbler said:

This MCB (yes, MCB, not RCD) is just 16A.

Your 2.3kW saw draws normally about 10A, more when it starts or is overloaded. Hardly a surprise that it trips the MCB occasionally and unpredictably.

Extension leads (unless they are faulty) have nothing to do with this.

Or it can be some fault with the saw.

Chainsaw was replaced by RIOBI after issue with another RIOBI same model. I opened pack now only use.

sujsuj

danrv said:

Try the Ryobi on a 32a circuit. That’s what I’m using for my Qualcast. 

How? wher I can find 32A ? Power sockets in kitchen..?

sujsuj

Eldi_Dos said:

sujsuj said:

Section62 said:

sujsuj said:

grumbler said:

Jonboy_1984 said:

They create additional resistance (and heat) when coiled due to the magnetic fields.

I think, magnetic field is a myth as cable has two cores with opposite currents.

And, again, heat (poor dissipation in this case) on its own cannot cause MCB tripping

RCD tripped

sujsuj said:

tripped switch highlighted

That isn't an RCD you've highlighted.  It is an MCB.

Move your wood pile closer to the power source... will be easier, safer and cheaper.

But I am cutting a tree branch!

Pruning saw would be cheaper and more efficient with the benefit you could use in damp conditions.

I got a Pruner and I think there is a saw attachment as well. But I thought it can be used for small branches only and manual labour more needed as well

sujsuj

Jonboy_1984 said:

They said on the second page its a garage socket, my guess is someone installed a pre-loaded consumer unit in the garage, and the unmarked 20A's are not connected to anything.

That is why I am wondering what else is plugged in on the same 16amp circuit.

For More clarity, I tried chain saw directly and with extension in 2 sockets...

1.  Garage socket , remember there is a connection from Garage to the Gate control CAME as well. CAME control is always plugged  & ON. When I tried direct  chainsaw in socket it worked and MCB tripped when connected with extension.
2. Conservatory Socket - There was a exercise Vibration machine also  worked from that socket, but tried after removing that machine only. When I tried direct  chainsaw in socket it worked and plug 13A fuse spoiled  when connected with extension.

I may have to try again to see if same results again. Also I have a third extension cable to be tried though it is smaller 10M one.

sujsuj

Jonboy_1984 said:

Are there any other devices on the same circuit (i.e. they also lose power when the switch goes to off). If so what are they?

Will try again tomorrow.

sujsuj

ThisIsWeird said:

Ah. That that whole CU is in the garage? 
Oops.

Yes, but there is a main one in the kitchen as well.

ThisIsWeird

sujsuj said:

Jonboy_1984 said:

They said on the second page its a garage socket, my guess is someone installed a pre-loaded consumer unit in the garage, and the unmarked 20A's are not connected to anything.

That is why I am wondering what else is plugged in on the same 16amp circuit.

For More clarity, I tried chain saw directly and with extension in 2 sockets...

1.  Garage socket , remember there is a connection from Garage to the Gate control CAME as well. Game control is always plugged  & ON. When I tried direct  chainsaw in socket it worked and MCB tripped when connected with extension.
2. Conservatory Socket - There was a exercise Vibration machine also  worked from that socket, but tried after removing that machine only. When I tried direct  chainsaw in socket it worked and plug 13A fuse spoiled  when connected with extension.

I may have to try again to see if same results again. Also I have a third extension cable to be tried though it is smaller 10M one.

A 13A fuse blew when you used the socket in the conservatory? 
There is surely something more amiss here? 
'Fuses' are relatively slow- blowing, so I'm struggling to think of what condition - other than a fault with the extension cable - could make this happen.
Yes, two cables are seemingly affected, but I've just had two PV inverters come up with the exact same - and very unusual - fault within minutes of eachother. That blew my mind, nevermind anything else.