New yellow book

[bernardgreen]

(beyond the fact that metal is clearly 'non-combustible').

Sodium is a metal. as is Magnesium. wire wool burns. And mercury is also a metal.

So to it is inadequate to specific metal as being non inflamable without also specifying which metal, environment and mode of use.

I seem to recall one reason for changing to plastic was the advantage that plastic does not rust and with metal CUs rusting away in damp basements the use of plastic to replace them was a big improvement.

 

[ban-all-sheds]

There is hardly anything in the world that someone cannot make a little worse and sell a little cheaper, and the people who consider price alone are that person's lawful prey.

 

[JohnW2]

(beyond the fact that metal is clearly 'non-combustible').

Sodium is a metal. as is Magnesium. wire wool burns. And mercury is also a metal. So to it is inadequate to specific metal as being non inflamable without also specifying which metal, environment and mode of use.

I assumed that those with an interest in what I was writing about would be familiar with the wording of Amendment 3, and therefore did not 'spell out' what it says. As I would have expected you to know, the (one) example given (in Amd3) of a material which is considered to be 'non-combustible' is ferrous metal. We don't even know whether aluminium would satisfy them.

Kind Regards, John

 

[PBC_1966]

40 Years ago you could have had a federal stab-lok

Certainly, there have been some bad designs in the past: Federal Pacific and Zinsco got a terrible reputation for various problems with breakers not tripping, overheating connections to the busbar etc. In the case of FPE, I think it turned out that some of their designs had not been properly submitted to UL for testing and their UL listing for the boards was withdrawn (sometime in the 1980's I believe). There are now Zinsco replacement breakers available to alleviate the earlier problems, but they're pretty expensive (i.e. up to $40 for a regular single-pole breaker), so unless you only need one or two it would probably be cheaper to replace the entire board.

But seriously... why do the insides of all US boards look similar to the boards we had here in the 70s with plenty of un-shrouded parts inside? I would have throught that in a country where people sue each other over the drop at a hat that there would be some pressure to improve in a similar way to the boards over here?

I like the fact that you can still get at everything here without having to half dismantle the unit. And there isn't a problem with cables coming loose from the main lugs! Obviously you need to be a little more careful when working in a live panel, but I can't help feeling that in the U.K. they've really started taking it a little too far these days.

Those look very similar to the Square D QO-X range which are sometimes found on installations 30-35 years old here. They are often unsuitable due to being type 4 and the max zs not being met. Do USA breakers have any type of type classification on the magnetic trip... or is it one type fits all?

There's no specific type classification similar to that used in the U.K. (old or new system). The manufacturers do publish characteristic curves for coordination in larger installations.

By way of trivia, the QO designation was chosen when the range was developed in the 1950's as standing for "Quick Open."

 

[ban-all-sheds]

There's no specific type classification similar to that used in the U.K. (old or new system). The manufacturers do publish characteristic curves for coordination in larger installations.

So the NEC contains no requirements for disconnection times?

 

[PBC_1966]

So the NEC contains no requirements for disconnection times?

Not set out explicitly, so far as I'm aware, although the last edition I've really looked at in detail is 2005, so there's a chance something has been added in the three editions since then. Circuit breakers will need to comply with certain minimum characteristics in order to pass UL listing, though, so I'm certain there will be maximum trip times based on specific criteria in those standards.

 

[JohnW2]

So the NEC contains no requirements for disconnection times?

Not set out explicitly, so far as I'm aware, although the last edition I've really looked at in detail is 2005, so there's a chance something has been added in the three editions since then. Circuit breakers will need to comply with certain minimum characteristics in order to pass UL listing, though, so I'm certain there will be maximum trip times based on specific criteria in those standards.

Even over here, the speed of disconnection is primarily a matter of the characteristics of the device, which presumably are defined in the relevant Standards. Eet in terms of MCBs/RCBOs, the 'requirements' we talk about (e.g. 'maximum Zs to achieve required disconnection times') are really in relation to the minimum current required to trip the magnetic part of the device - once tripped, the speed of disconnection is down to the device.

Kind Regards, John

 

[ban-all-sheds]

The point is that if the time/current curves of the breakers are unknown and/or to no particular standard, you can't have mandated tripping times, as nobody would know which breaker to use. A problem compounded by the lack of loop testing in the US.

 

[Adam_151]

The point is that if the time/current curves of the breakers are unknown and/or to no particular standard, you can't have mandated tripping times, as nobody would know which breaker to use. A problem compounded by the lack of loop testing in the US.

Which is similar to the situation here in the 60's and 70's... loop testing equipment did exist, but was very primative and would not have been assessible to most contractors (nor would they understand how to use it or the significance of the result). It was just a case of match the fuse size to the cable and load, in all fairness I guess the number of issues when re-wireable fuses were used, was not high. Problems came when breakers started coming in and some of the earliest ones fell into type 4 and the same thing happened. Type 4s were being chucked in indescriminatly up until the early 80's. In 2015 we are still replacing boards which are unsuitable.

I do wonder when the US will catch up!

 

[PBC_1966]

Which is similar to the situation here in the 60's and 70's... loop testing equipment did exist, but was very primative

I'd put my 40-year-old Clare loop tester up against any of the latest instruments and challenge anyone to get a more accurate and meaningful result from the latter.