Advice on TABLE 41.3 please?

[John Lundrigan]

Table 41.3 provides max Zs values based on Uo = 230V. Can this this table be used to assess Zs for Uo = 110 v ac on a reduced voltage system. Perhaps reducing Zs pro rata?

Thanks

 

[westward10]

See Table 41.6

 

[Risteard]

Uo is not 110V for an RLV system. It is 55V for a single phase (split phase) system or 63.5V for three-phase.

 

[westward10]

Uo is not 110V for an RLV system. It is 55V for a single phase (split phase) system or 63.5V for three-phase.

I am guessing that is what he means.

 

[Strima]

Zs=Uo/Ipf???

 

[Wilko]

As the devices are current based the max Zs may be scaled using Mr Ohms and his Law.

 

[westward10]

Use Table 41.6 assuming Uo is 55 or 63.5v.

 

[John Lundrigan]

Thanks for the excellent information. I realise that the 110 volts relates to 55V between the line and centre tap of the output of the transfer providing the reduced low voltage. Table 41.6 for a Type C breaker at 50 A does specify 0.10 ohms. This is about a quarter of that for the same breaker in a low voltage circuit (as I had suspected). In fact in the previous version of BS 7671 it was exactly a quarter.

Thanks again for taking the time to explain.