Educating, Investing and Simplifying BS EN 61439 - Temperature Rise

Temperature Rise? I2R losses surely it’s just hot air. Exactly.

Loose wires cause fires, why? …….Heat. Connections create resistance which creates heat, the more connections the more heat. Simples, it’s physics, marketing teams can wrap up offers, solutions but physics hasn’t changed and current-carrying conductors produce heat and it’s the single most important consideration when designing switchgear! Why, because if you can’t handle the heat you get out of the kitchen, otherwise you start to ‘derate’. Switchgear is exactly the same but instead of a nice dip in the pool or a cool crisp beer, switchgear has no choice it starts to derate which reduces the efficiency of your system, increases mean time between failures, damages equipment, increase costs in various areas and quite simply fails. Not what you want from your beating heart of the electrical infrastructure, if your Main Switchboard is offline, so is everything else.

Example time,

So, not to pick on Schneider, but they are the market leaders, commonly referred to as the best overall range and products on the market. To me that gives me the right to pick on them.

Don’t take this as an endorsement for other manufacturers, they are no better. You have to know your manufacturer, who’s job is that – the Manufacturer.

So - 4000A (MTZ2) Draw-Out, Air Circuit Breaker (ACB)

So what do we know from the description:

Withdrawable ?

it’s an ACB ?

4000A Rating X, what how come?

Discrepancies, discrepancies, discrepancies! between nominal ratings and actual ratings, so what’s the point in nominal ratings, why don’t they give us actual readings! You may have to ask marketing about that, but the actual answer is because it's less! Also because its down to the manufacturer to deliver the actual results within the complete enclosure and copper busbar system. We are now getting into complete solutions, this is important.

ACB in Open Air

ACB in Enclosure

As you can see it’s a completely different animal when its been nicely tucked up in a ‘snug’ compartment.

Think of it like this, Example time,

Toaster, on your kitchen counter, does the job… designed to be put on your counter and we could class this as ‘open-air’, the toaster toasts our bread and off we go, no issues. Take that toaster, put it in a cupboard, just slightly larger than the toaster, no ventilation and shut the door, where does the heat go? Why is the bread black when we bring it out? How long is the toaster going to last in these conditions? Is it the same toaster we had in the kitchen. You are starting to understand.

Less about toast, back to the objective in hand, Is it still a 4000A? Where does the heat go? Is my breaker toasting away? How do I know it’s still capable of delivering the solution I want?

Temperature Rise Testing, an essential test of BS EN 61439 (Governing British Standard (& currently European Norm – Careful) of Low Voltage (L.V) Switchgear). It’s our bible, our directive and it’s the standard.

Temperature Rise Testing

Let’s stick with our good old friend, 4000A, let’s stick with the market leader, Schneider. So - 4000A (MTZ2) Draw-Out, Air Circuit Breaker (ACB), let’s class this as ‘Open Air’

Let’s stick this in our enclosure, with our chassis, doors, shelves, dividers, gland plates, ventilation systems, lifting facilities, supports, other breakers, copper busbar droppers, copper busbar risers, copper busbar breaker connections, mechanical bracings, the list goes on... Then let’s shut to doors, zip up the covers, ready for service. Waiting is my 4000A still 4000A? It was (we think) a 4000A breaker before I added all the rest of the bits and bobs, before I actually turned this component into a product. How do I know? Test it.

Here’s our ACB in Open Air  

Here’s our Product, now we are talking, starting to look like Switchgear now?

So what happens now, the completed product (important here – you are testing a product now, not a device, not a component, not the copper, not the enclosure, the complete product! We know what putting a 4000A label on a breaker does…) is hooked up to basically a massive temperature monitor, this is driven by the standards and more detail can be delivered into how this is done but it’s for another day, simply it tests the whole product and gives it a current rating. Excellent so I can now prove my 4000A does 4000As and it's all plain sailing. Yes basically, but it's not that easy. It took us 20 days of testing to get the 4000A to do 4000A, and this was only for one of our products, we use this breaker in 3No. product ranges and you have to test them all! We believe we are only one of two manufacturers who have achieved it. But surely that must be GR and Schneider, can you believe it, it’s not. The other manufacturer is only hearsay and without seen certificates that is as far as I go, but Schneider can’t achieve 4000A (MTZ2) from their own breaker!!

It's about to get more complicated but we are keeping it simple, why are their loads of values, why does it say 3320A & 3700A and even 2960A!! That’s really low! Yes it is, here we have our friends,

Degrees Celsius = °C & Kelvin = K, °C we are all comfortable and its what we measure temperature in, Fahrenheit is gone lets all move on. K is the measure of absolute temperature, so yes this is real temperature and not °C which is relevant to water (Freezing 0°C & Boiling 100°C). K is the absolute scale of temperature where zero is zero, no other temperature exists below zero, where molecule energy is 0 (or minimum). So that’s technical over, K is therefore used for temperature rise for differences/intervals in temperature.

So what do we know, that got technical there. We know the 4000A device creates heat, we know the busbar connected to the devices creates heat, we know the enclosure and the mechanical structure keeps the heat from escaping and restricts airflow. The one item we must link this to ambient temperature (typically manufacturers will restrict ambient temperature to a maximum of 35°C (It’s in the British Standard), as this is what they have/should have tested too. This is why we need ‘K’ and that’s my last on that I promise.

4000A switchboard, in the case of GR’s test, was tested at 4000A per phase, delivering what the breaker was developed for, utilising ventilation – NOT FORCED ONLY NATURAL (thought I would get that in there) and lots of clever utilisations of copper designs, natural airflow to create a solution that delivers exactly what it says on the tin, back to comfort, back to a system that delivers and works!

From this, a certificate is created and issued to what the product can do, its that simple. Everyone has got one…… no, no they haven’t. They should, but they haven’t. Many manufacturers aren’t adhering to the standards and even worse I am seeing IP66 rated boxes for ACB’s that only two manufacturers (that I know of) have passed them in IP3XD or IP31D enclosures. Industry slating over.

It’s worth saying that Temperature Rise is a test of the product, not the breaker, not the busbar, not the enclosure, it’s it all together and your panel should be based on this certificate. From my temperature rise experience if you assume these breakers, be it ABB, Schneider, Chint, Eaton, Siemens… the list goes on, do what they say on the tin. You aren’t a manufacturer, you aren’t delivering BS EN 61439 solutions, you are misleading your clients and your products aren’t fit for purpose. Temperature Rise Certifications are 100% required on all your switchboards.

All I can advise is know your manufacturer, if you ask them about ‘Annex D’, temperature rise and they look at you blank, you are dealing with the wrong people, read the small prints, ask the questions, gain the confidence.