adiabatic test

[D Skelton]

some great psuedo physics going on here.
wake me up when you get to thermodynamics.
;-)

I've looked over this post a few times and I must be missing something. I don't get it, please tell

 

[ib60]

many thanks everyone for your assistance it has been most helpful

 

[Guest55]

....... I don't get it,

oh , i thought you were well versed in the subject after posting....

There is more than one adiabatic equation

;-)

 

[Chr!s]

I've looked over this post a few times and I must be missing something. I don't get it, please tell

Don't worry, your pretty much there, I'm sure Biff will expand further.

 

[D Skelton]

oh , i thought you were well versed in the subject after posting....

When I said I've looked over 'this' post, I was referring to your post regarding pseudo physics, not my own. I'm more than comfortable with the info I posted, I just didn't get the joke you made or what you were referring to. Sorry, am I a bit slow?

Also, I get the impression you are implying that I'm wrong when I say there is more than one adiabatic equation?

Don't worry, your pretty much there, I'm sure Biff will expand further.

I don't believe I missed anything hence why I'm not really worried, please do explain...

 

[ackbarthestar]

Thermodynamics, my rear orifice We are talking about a non-thermal response.
Now,
Why do you think C types were used in the first place?

5-10In for type C breakers. If in doubt apply manufacturer's data.

Although, you could decrease R2 by cross bonding the circuits.

 

[Risteard]

A high Zs can be dealt with by means of supplementary bonding. However, the purpose of this is NOT to reduce Zs through parallel paths but to keep the voltage to a safe level until disconnection occurs.

Thermodynamics, my rear orifice We are talking about a non-thermal response.
Now,
Why do you think C types were used in the first place?

5-10In for type C breakers. If in doubt apply manufacturer's data.

Although, you could decrease R2 by cross bonding the circuits.

 

[ackbarthestar]

A high Zs can be dealt with by means of supplementary bonding. However, the purpose of this is NOT to reduce Zs through parallel paths but to keep the voltage to a safe level until disconnection occurs.

Well, maybe thermodynamics is appropriate, well the 2nd law at least,. The temperature is rising.:wink_smile:

Yes, it does both, but you've already stated that.......

 

[johnboy6083]

As said, you have a few options open to you. Supplementary bonding is one option, using a device with a lower rating is another. A combination of the two is also acceptable. Using an RCD is allowed, but in my personal opinion it's the absolute last resort.
the adiabatic equation which is transposed to give you the time it takes for a cable to reach limiting temperature is used to ensure that a fuse is suitable for protecting a cable against short circuit. This is often used (or should be) to ensure cables from busbar chambers ect will be able to take the very high fault currents generated until the upstream device operates.

 

[ackbarthestar]

As said, you have a few options open to you. Supplementary bonding is one option, using a device with a lower rating is another. A combination of the two is also acceptable. Using an RCD is allowed, but in my personal opinion it's the absolute last resort.
the adiabatic equation which is transposed to give you the time it takes for a cable to reach limiting temperature is used to ensure that a fuse is suitable for protecting a cable against short circuit. This is often used (or should be) to ensure cables from busbar chambers ect will be able to take the very high fault currents generated until the upstream device operates.

I personally wouldn't go down the path of changing the breaker size or type unless the design is flawed to begin with.
Otherwise we are left with
1/ decrease R2
2/ Use of RCBOs but then that is a flawed in its necessity to correct a flawed design

A good design to begin with is the answer

 

[bigm]

Hi,
First of all forget about doing the adeabatic calculation , its only for calculating sizes of C.P.C's. It seems that you are concerned about going over the max permitted Zs values in BS7671, you are quite right to install RCBO's @ 30mA - this means your max values of Zs for each circuit can go as ihgh as 1667 ohms and technicaly the RCBO will disconnect within 0.4 seconds for fault protection - the type of RCBO makes no difference at all so install what suites the type of load. Overload protection is provided by all RCBO,s after all the abbreviation stands for RESIDUAL CIRCUIT BREAKER WITH OVERLOAD PROTECTION.

CHEERS.

 

[D Skelton]

Hi,
First of all forget about doing the adeabatic calculation , its only for calculating sizes of C.P.C's.

Like I demonstrated before, there is more than one adiabatic equation.

your max values of Zs for each circuit can go as ihgh as 1667 ohms

7667 ohms for a TN system.

you are quite right to install RCBO's @ 30mA

Why is he limited to 30mA? He could install 1000mA RCBOs and still have 230ohms to play with as a max Zs. 30mA provision is only needed when the regs require additional protection.