Combining Rating factors
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- Опубликовано: 26 сен 2024
- When designing electrical installations, part of the process involves selecting rating factors that are needed to adjust a conductors tabulated current carrying capacity to accommodate the differing factors that the unique method of installation has introduced.
If we just select all of the appropriate rating factors within a cables run however, we may waste our design and oversixe cable selections (probably complying with future 18th edition Part 8 in the process).
This video just illustrates how to determine which rating factors we should use when carrying out our designs.
Spot on video shouldn't expect anything less from you. Just in the process of showing my apprentice cable calcs and was looking for material to help me to get the point across. 👍
This is a really good video Sparky Ninja! I'll be using it to pass on to anyone who wants to understand grouping factors
Why in the on-site guide does it not explain this? As you read it it tells you to do the opposite of what you say and divide In by ALL factors?
Thanks
Just bloody amazing. Thankyou
There is grouping factor (Cg) and reference method B (in trunking). Could you please help me how to approach this?
Great explanation Dave,
Ok so in short, you just pick the single worst (closest to 0) factor, or combination of factors that occur at the same time in the same place to a cable? That sounds straight forward👍
My question is why, in bs7671 do they show multiple factors on the bottom in the same formula, if you only need to pick the worst one(s)?
say there is a large installation with 20 circuits in trunking leaving the DB. That would mean a grouping factor is 0.38… this would make every cable need to be very large, nevermind if other factors were applicable ? Is this right, anyway around this?
don't put 20 circuits in trunking?
thanks SparkyNinja. I would like to ask when is the grouping factor is taken into account ? I understand it would be during the design stage, assuming a new building. However, would the designer know the cable routing ? unless you tell the contractor that a conduit must not have more than 4 circuits or something.
It would be done at the design stage, the assessment of general characteristics in Part 3 push on the need to collect all necessary information.
Communications with project managers and allied trades is important here.
Also depends if your using a circuit breaker or rewirable fuse as the rewritable fuse adds another factor, so if you use a circuit breaker the factor is reduced even more equating to smaller cable
0.725 👍
That made so much more sense then when you read it out the manual to your self lol
Another great video! Can I ask what your opinion is of the EAL 4337 and 4338 courses?
Hi HobbyMan UK, thanks.
Sure, the EAL I&T courses in my opinion are designed better, the assessments are fairer - but not necessary simpler. If I had the option I would deliver the EAL over the C&G in almost every subject partly because of the qualification structure but also because of how the EAL are as an accrediting organisation. Unfortunately C&G is the common asked for qualification in the industry (2391 etc) and so I have found many places that deliver the 4337/38 are actually using the C&G assessment rigs and material as a baseline, which I think is unfortunate.
SparkyNinja thanks for your quick response. Looking at some of the courses they do and wasn't sure on the EAL reputation.
Great video I've been racking my brain about this, you have really simplified it for me thanks
great
Thanks, this is not how it was explained to me in college.
Cheers Gary, hopefully it makes sense.
Yes, only multiply correction factors together if they are effecting the cable on the same section of cable :)