overloads

[lowcool]

Motor contactor overloads.do we need them ?

[Grizzly]

Why would you dispute their necessity?
Without them you would see far more welded contacts and excessive fire / arching damage.
Grizzly

[lowcool]

sorry grizzly i will edit and make it motor contactor overloads.
the reason for my thought was it has always been best practice especially were warranty is concerned.have seen alot of a/c units with contactor and relying on the internal overload of say the hermetic types compressor motor windings.
Circuit protection is more adequate than in previous times and overloads should trip in your scenario with an uneven leg load but usually dont causing the welded contacts as its application is winding protection.i cant think of any internal compressor motor that has caused welded contacts,ive seen the results of explosions of contactors caused by a compressors.

just thought it might make interesting discussion.
i can go jump in the lake if anyone insists

[Grizzly]

Having explained further, Your questions are indeed Valid!
No need to search out Water just yet!
Grizzly

[frank]

Here in the UK, it is a requirement of BS7671-2008 (552.1.2) that all electric motors having a rating exceeding 0.37kW shall be provided with control equipment incorporating means of protection against overload of the motor. So a motor overload is mandatory if your installation is to comply with the regs.

Another little known fact is the requirement to provide a main bonding conductor to air conditioning systems (411.3.1.2). How many comply with this I wonder?

[Brian_UK]

Regardless of the legalities I would always weigh up the cost difference of paying for an overload or a burnt out motor due to some form of overload condition.

Take the case of a ventilation fan motor that starts to run over current because there is excess air being handled by the fan - access door left open eg. Overload stops the motor running before it is damaged or killed.

They will also give an early warning of pending failure by tripping prior to total shut-down. (Well, sometimes)

[lowcool]

what if the motor had its own internal overload or thermistor.wouldnt mind hearing from a manufacturer on this one.it was an earlier post on setting a bitzer overload that got me rethinking about this.

frank pardon my ignorance but what is a main bonding conductor

[Grizzly]

main bonding conductor

Earth wire to the rest of us!
Also known as the CPC I believe?
Is that correct Frank?
Grizzly

[frank]

what if the motor had its own internal overload or thermistor.wouldnt mind hearing from a manufacturer on this one.it was an earlier post on setting a bitzer overload that got me rethinking about this.

frank pardon my ignorance but what is a main bonding conductor

I guess you are familiar with electrical installations?

It is the conductor between the main earthing terminal (sometimes the copper earthing busbar) and say, the gas main, water main, steelwork structure .....

[frank]

main bonding conductor

Earth wire to the rest of us!
Also known as the CPC I believe?
Is that correct Frank?
Grizzly

The CPC (Circuit Protective Conductor) is the earth conductor on a 'circuit' Grizzly.
The Main Earthing Conductor is the earth cable from the Main Earthing Terminal (MET) (copper busbar or earthing terminal in the dist board) and the point where the supply enters the premises (meter)
A Main Bonding Conductor connects the gas, water, steelwork to the MET.

Sorry Grizzly, no lolipop this time

[Grizzly]

The CPC (Circuit Protective Conductor) is the earth conductor on a 'circuit' Grizzly.
The Main Earthing Conductor is the earth cable from the Main Earthing Terminal (MET) (copper busbar or earthing terminal in the dist board) and the point where the supply enters the premises (meter)
A Main Bonding Conductor connects the gas, water, steelwork to the MET.

Sorry Grizzly, no lolipop this time

Sorry Frank
I was so eager to answer, I forgot the basics.
I was once questioned by a MEB inspector as to why the sink draining board was not Earth Bonded.
In fairness to him in those days composite ones that looked like metal were pretty rare.
It was the same job as to where my mate the sparky.
Blew his favourite "Elliot Lucas" pliers up. Cutting out old cables.
When the main incoming 100a fuse had been removed.
Discuss!
Grizzly

[Quality]

I was once questioned by a MEB inspector as to why the sink draining board was not Earth Bonded.

Grizzly

Now that is a supplementary bonding conductor or even an equipotential conductor depending on the installation and or test results

Earthing if all goes well it is never used but god forbid when its in need your glad its there

[glenn1340]

[quote=lowcool;206496]what if the motor had its own internal overload or thermistor.wouldnt mind hearing from a manufacturer on this one.it was an earlier post on setting a bitzer overload that got me rethinking about this.


Thermistors are ok for detection of heat build up in motors up caused by cooling problems or excessive load etc but in my experience they`re no good for phase failure or motor stalling as by the time the thermistors pick up high temperatures the damage has been done.
If thermistors are only used I like to fit an oveload and wire them in series. That way the motor`s protected for stalling AND gradual overtemperature problems.

[monkey spanners]

It was the same job as to where my mate the sparky.
Blew his favourite "Elliot Lucas" pliers up. Cutting out old cables.
When the main incoming 100a fuse had been removed.
Discuss!
Grizzly

Main incoming live and neutral round the wrong way so the 100A fuse was in the neutral.....

Jon

[lowcool]

not allowed to earth bond to pipe steelwork etc here.its an earth stake in the ground

[frank]

not allowed to earth bond to pipe steelwork etc here.its an earth stake in the ground

You must be on a TT system then, the same as our caravan parks.

[Grizzly]

Main incoming live and neutral round the wrong way so the 100A fuse was in the neutral.....

Jon

On the main incomer before the meter. Highly unlikely!
This was on a 1930s Cottage with a PME system if I remember correctly.
Anyway the sparky involved was a fully indentured highly competent Guy.
We reckoned at the time that there was a supply "Tapped of of the adjoining cottage.
As ours was semi detached.
We never did find out for sure. Made a nice hole in his side cutters/ pliers though.

Grizzly

[frank]

"Tapped of of the adjoining cottage"
Grizzly

More than likely tapped off the lampost outside
Then again, maybe you don't live on our estate

[monkey spanners]

I've seen main live and neutral into the fuse box round the wrong way on farms a few times, 100A fuses replaces with nails, other fuses with fencing wire or tin foil, once a whole steel framed parlour and dairy was live when the genny change over switch shorted out, earth leakage trips with bypass switches because it wouldn't stay on when it rained....

Nothing would surprise me

Jon