Maximum Demand exceeded

[GM at CA UK]

If it is of any interest I just wrote an article about maximum demand measurement as an alternative to diversity calculations following a case study on a multi-occupancy building in Richmond, London (5 flats in a converted house of 50 years). It has a single phase 100A supply split into 6 and in a 2 week log the maximum current drawn was 48.83A, and that was only for 2 minutes during an evening. The article is in Energy Manager Magazine and can be read here https://issuu.com/abbeypublishing/docs/em_may_2023/22

 

[SPECIAL LOCATION]

If it is of any interest I just wrote an article about maximum demand measurement as an alternative to diversity calculations following a case study on a multi-occupancy building in Richmond, London (5 flats in a converted house of 50 years). It has a single phase 100A supply split into 6 and in a 2 week log the maximum current drawn was 48.83A, and that was only for 2 minutes during an evening. The article is in Energy Manager Magazine and can be read here https://issuu.com/abbeypublishing/docs/em_may_2023/22

Cheers.. Yes interesting and relevant to the topic in hand....
And confirms just how inaccurate various estimated max demand calculations can be.

 

[Sharpend]

Great write up.

 

[Mike P]

A very good and thorough report. My only question would be, what happens in extreme and high days and Hollidays (say Christmas) when the load could be excessive as a one off? I agree with the introduction of LED and more economic appliances, the loading will improve on a day to day basis, but the one offs!!

 

[mort2376]

A very good and thorough report. My only question would be, what happens in extreme and high days and Hollidays (say Christmas) when the load could be excessive as a one off? I agree with the introduction of LED and more economic appliances, the loading will improve on a day to day basis, but the one offs!!

The "Christmas Day" scenario just means the system may draw more than 100a but only for short periods.

If, as in the article its worked for a considerable number of years then it's unlikely to fail soon.

I find it odd that appliances are using less and less power, but we seem to be installing bigger consumer units.

There are still properties out there with 3 or 4 way consumer units running 1x light, 1x sockets a cooker and maybe an immersion or shower. We replace it with a 14 way board and worry as the max demand calc doesn't work !!!!

Looking at the fuse characteristics charts I'm thinking a 100a 1361 will happily get warm but not blow upto 150-175a. This allows for the small peaks of excess. It takes 5 seconds to blow it drawing 650a !

 

[GM at CA UK]

The "Christmas Day" scenario just means the system may draw more than 100a but only for short periods.

If, as in the article its worked for a considerable number of years then it's unlikely to fail soon.

I find it odd that appliances are using less and less power, but we seem to be installing bigger consumer units.

There are still properties out there with 3 or 4 way consumer units running 1x light, 1x sockets a cooker and maybe an immersion or shower. We replace it with a 14 way board and worry as the max demand calc doesn't work !!!!

Looking at the fuse characteristics charts I'm thinking a 100a 1361 will happily get warm but not blow upto 150-175a. This allows for the small peaks of excess. It takes 5 seconds to blow it drawing 650a !

The short term exceeding of the fuse/cut-out rating is an interesting one. I'm just writing up another case study from a pub with rented rooms above it, all on a single phase 100A fused supply, where a 3 week log showed a max current draw of 126.6A, which occurred one evening but only spanned a period of a few seconds. There were several events where the current drawn exceeded 100A for a number of minutes, and one particular evening where it exceeded 100A for approximately 4 hours. As per the fuse characteristics you mention, none of these events were enough to blow it.

 

[unphased]

Sorry, but there is a misunderstanding through this thread about what maximum demand means, that maximum demand is somehow related to the number of circuits or the rating of the cut-out. It is just a theoretical load on an installation that it may experience as a peak at any one time. Nothing whatsoever to do with the number of circuits or the size of the cut-out. I hope the OP understands the absurdity of his title for the post now? Maximum demand Exceeded! That is such a naive statement. MD is whatever it is. To calculate what it might be takes a lot of thought and experience so it is very often over estimated. Those who say "clamp the tails" and measure it are nearly right but that will only tell you the load on the tails at that particular time. The best answers are the ones who are measuring it over a long period. Cut-out fuses do NOT give you maximum demand they will fail if their RATING is exceeded. Fuses can carry much more than their rated current for short periods. But its not maximum demand! Some circuits will regularly carry higher currents than others and some no current at all for long periods. It's naive to count the fuse ratings and add them up. That is just daft. I hope that people reading this thread will grasp a better understanding of what it actually is. Many of you have, but some clearly haven't.

 

[Leigh Winspear]

Sorry, but there is a misunderstanding through this thread about what maximum demand means, that maximum demand is somehow related to the number of circuits or the rating of the cut-out. It is just a theoretical load on an installation that it may experience as a peak at any one time. Nothing whatsoever to do with the number of circuits or the size of the cut-out. I hope the OP understands the absurdity of his title for the post now? Maximum demand Exceeded! That is such a naive statement. MD is whatever it is. To calculate what it might be takes a lot of thought and experience so it is very often over estimated. Those who say "clamp the tails" and measure it are nearly right but that will only tell you the load on the tails at that particular time. The best answers are the ones who are measuring it over a long period. Cut-out fuses do NOT give you maximum demand they will fail if their RATING is exceeded. Fuses can carry much more than their rated current for short periods. But its not maximum demand! Some circuits will regularly carry higher currents than others and some no current at all for long periods. It's naive to count the fuse ratings and add them up. That is just daft. I hope that people reading this thread will grasp a better understanding of what it actually is. Many of you have, but some clearly haven't.

Has this post not created learning for us all?

Why pick at people calling them absurd for wanting to learn more about our trade?

The loose, title refers to the method I was taught to consider and I show that source also and refer to the regulation considerations, or someone else does as part of the solution.

I have learned loads, hehe, from this thread and guidance has been applied from most posters, but there is always a bit ch from someone such as yourself which spoils this forum too often.

 

[unphased]

Oh come on! In what way is it bitchy? In my experience there is always someone like you who chooses to bit ch back! The need to do that is odd. I thought this was supposed to be friendly forum? Do you want to explain yourself since you think I am spoiling it for you? Can't see any bitchy comments in my post myself.

 

[Chewbacca]

Ok this thread is starting to get personal, so I'm applying the force.