W
walberto
I'm a qualified spark but studying building services engineering at uni and just need a little bit of advice to see if I'm going wrong.
Trying to answer a question where we have a 16A Type B MCB, and a short circuit fault current of 153.37A. From fig 3.4 of regs we can see that for a fault current of 80A or over the breaker will activate in 0.1second or less. However we are asked if this could be changed to a 16A Type C MCB (in terms of the short circuit fault current). Putting the thermal constraints of the cable to one side, I am more concerned with working out exactly how long it would take for this type of breaker to activate with a fault current of 153.37A. From looking at the regs (Fig 3.5 of the 17th edition without the latest amendment) I would have thought you could plot this on the chart, giving a tripping time of more than 5 seconds. I would have thought this did not comply as any circuit of rating less than 32A needs to trip in under 0.4 seconds.
I could be totally wrong so I wouldn't mind a comment or two to set me straight! Thanks in advance.
Trying to answer a question where we have a 16A Type B MCB, and a short circuit fault current of 153.37A. From fig 3.4 of regs we can see that for a fault current of 80A or over the breaker will activate in 0.1second or less. However we are asked if this could be changed to a 16A Type C MCB (in terms of the short circuit fault current). Putting the thermal constraints of the cable to one side, I am more concerned with working out exactly how long it would take for this type of breaker to activate with a fault current of 153.37A. From looking at the regs (Fig 3.5 of the 17th edition without the latest amendment) I would have thought you could plot this on the chart, giving a tripping time of more than 5 seconds. I would have thought this did not comply as any circuit of rating less than 32A needs to trip in under 0.4 seconds.
I could be totally wrong so I wouldn't mind a comment or two to set me straight! Thanks in advance.