Do I need over current protection?

[mjbarcelona]

Hi guys, i'm working on some project, do i still need over current protection if i'm using a soft starter and do I still need circuit breaker for that motor???

 

[telectrix]

if it is a fixed load, you could dispense with overload protection, but still need fault (short circuit) protection

 

[Deleted account]

if it is a fixed load, you could dispense with overload protection, but still need fault (short circuit) protection

I understand with a fixed load there is no chance of overload, but surely the short circuit protection will automatically give overload protection anyway even if it doesn’t need it.
Am I missing something?

 

[telectrix]

I understand with a fixed load there is no chance of overload, but surely the short circuit protection will automatically give overload protection anyway even if it doesn’t need it.
Am I missing something?

no.you could have. say, a 2.5mm cable (27A CCC) protected by a 50A MCB giving fault protection, but the 50A MCB will not provide overload protection to the cable.

 

[Baddegg]

Was pondering that myself....good explanation @telectrix

 

[netblindpaul]

Upstream of the soft start, yes, downstream, no the soft start should be programmed to limit the overload current, if not the soft start instructions must give you the data you need.
Just remember if it's machinery BS7671 is irrelevant.

 

[littlespark]

OP isn’t in UK? (Correct me if I’m wrong) So BS7671 is irrelevant anyway.

 

[netblindpaul]

OP isn’t in UK? (Correct me if I’m wrong) So BS7671 is irrelevant anyway.

You're right, I saw the flag under his name and saw the little Union Jack and thought it was the whole flag, not just the small bit in the corner!
IEC 60364 still applies in AUS/NZ though it is a local interpretation like 7671, as would IEC 60204-1 which isn't so local.

 

[Megawatt]

Hi guys, i'm working on some project, do i still need over current protection if i'm using a soft starter and do I still need circuit breaker for that motor???

The soft start should have your overloads built in it you just have to read the manual and set to probably 115% X the full load of the motor and YES you have to have a circuit breaker for the soft start and motor

 

[SheffSimon]

Overload should be set to motor FLC. Job done.

 

[Megawatt]

Overload should be set to motor FLC. Job done.

Sheff you left out the short circuit protection

 

[netblindpaul]

Sheff you left out the short circuit protection

Motor overloads are set to motor FLC in the IEC world, settings in the NEC world maybe different.

 

[davesparks]

The soft start should have your overloads built in it you just have to read the manual and set to probably 115% X the full load of the motor and YES you have to have a circuit breaker for the soft start and motor

Why would you set to 115% of the FLC for a soft start?
Normally you set overloads to the FLC for DOL etc.

 

[Megawatt]

Why would you set to 115% of the FLC for a soft start?
Normally you set overloads to the FLC for DOL etc.

Not sure about the soft start, but they are usually sized ( 5hp 10hp ) so you have to put all the settings in. As
for the 115% is in article 430-250 of the NEC motors rated at 1.15 service factor is 125% Dave in the US we are taught to use the FLA on the motor and multiply it by 125%. All other motors multiply them by 115% the only information we use off the nameplate is the HP then you go to table 430-32(a1) of the NEC and find your hp and that’s where you get your amperage for that motor not the amperage on the
[automerge]1567306941[/automerge]

Not sure about the soft start, but they are usually sized ( 5hp 10hp ) so you have to put all the settings in. As
for the 115% is in article 430-250 of the NEC motors rated at 1.15 service factor is 125% Dave in the US we are taught to use the FLA on the motor and multiply it by 125%. All other motors multiply them by 115% the only information we use off the nameplate is the HP then you go to table 430-32(a1) of the NEC and find your hp and that’s where you get your amperage for that motor not the amperage on the nameplate

Dave I get what your saying on setting them in a soft start because it doesn’t have the in rush current a standard motor does. I’m not an expert on soft starts so I could have misquoted thinking about it

 

[davesparks]

Not sure about the soft start, but they are usually sized ( 5hp 10hp ) so you have to put all the settings in. As
for the 115% is in article 430-250 of the NEC motors rated at 1.15 service factor is 125% Dave in the US we are taught to use the FLA on the motor and multiply it by 125%. All other motors multiply them by 115% the only information we use off the nameplate is the HP then you go to table 430-32(a1) of the NEC and find your hp and that’s where you get your amperage for that motor not the amperage on the
[automerge]1567306941[/automerge]

Dave I get what your saying on setting them in a soft start because it doesn’t have the in rush current a standard motor does. I’m not an expert on soft starts so I could have misquoted thinking about it

There is a common misconception in the UK that overloads need setting at more than the FLC, but normally they should be set at FLC as they are designed so that they cope with the inrush fir that setting.