I have a main UPS power DB with ELR

[Histor]

I have a main UPS power DB with ELR (500mA). This main DB-01 feeding control supply to some PLC,VFD and a Sub UPS DB-02.

The Sub UPS DB-02 has multiple outgoing circuits with MCB and RCCB (300A) in each circuits.

Suddenly my UPS main DB-01 tripped by ELR. No RCCB tripped in sub UPS DB-02. How come ELR tripped before RCCB in sub DB?

 

[waross]

No unbalanced current.
An RCCB only trips when the outgoing current does not equal the return current.
When the currents are unbalanced the RCCB assumes that the current deficit is returning through a grouns path and trips.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Mr. Histor (Electrical)(OP)29 May 23 00:57
" #1.I have a main UPS power DB with ELR (500mA). This main DB-01 feeding control supply to some PLC,VFD and a Sub UPS DB-02.... #2. The Sub UPS DB-02 has multiple outgoing circuits with MCB and RCCB (300A) in each circuits...Suddenly my UPS main DB-01 tripped by ELR. No RCCB tripped in sub UPS DB-02. How come ELR tripped before RCCB in sub DB? "
1. DB-01 ELR (500mA) trips but DB-02 RCCB (300mA) did NOT trip, possible cause:
a) earth fault in some PLC, VFD.
b) wiring from DB-01 to some PLC, VFD having earth fault/low insulation to earth.
c) faulty ELR.
2. DB-02 RCCB (300mA) did NOT trip but DB-01 ELR (500mA) trips. Possible cause:
a) there is NO earth fault in amy outgoing circuits from DB-02.
b) see above 1. The earth fault is on the other loads NOT on the branch feeding to DB-02.
c) check all the RCCBs to ensure tripping at >150mA.
3. It has NOTHING to do with:
a) whether the loads are balance or unbalance, as it was (presumed) operating fine before.
b) in any 3-phase system, the lines can be balance or unbalance; but the vector sum of three lines + N MUST equal to ZERO; i.e. NO earth fault. The ELR and RCCB shall NOT trip when there is NO earth fault, irrespective whether the loads are balance or unbalance across the phases and Neutral.
Che Kuan Yau (Singapore)

 

[Histor]

What if all the 10 branch circuits leaks each 60mA which is less than it tripping setting (300/150mA) in DB-02 and it accumulates (10circuits X 60mA = 600mA) lead tripping ELR in DB-01? is it possible?

 

[che12345]

Mr. Histor (Electrical)(OP)29 May 23 06:14
" What if all the 10 branch circuits leaks each 60mA which is less than it tripping setting (300/150mA) in DB-02 and it accumulates (10circuits X 60mA = 600mA) lead tripping ELR in DB-01? is it possible? "
1. YES, possible.
2. In this case, it is more difficult to pin-point the culprit:
a) as every circuit seems to be having an acceptable low earth-fault current <150mA.
b) in DB-01, when the accumulated earth-fault >500mA. This may happen randomly.
3. Possible solution:
a) monitor the highest accumulated earth-fault current over a period of say a week to have a reasonable useful indication. Reset the ELR to slightly higher than the highest value recorded, if the system permits to trip >500mA.
b) in DB-01, add another ELR. Transfer some of the loads to the new ELR. This is to ensure that the accumulated load is <500mA. This would maintain the tripping at 500mA, the preferred/allowed value.
Che Kuan Yau (Singapore)

 

[Kiribanda]

ELR & RCCB are working on the same principle.
If your system is a 3-Ph/ 4-wire with neutral, then I need to see how the ELR is connected and how the RCCBs are connected in the 4-wire system
before I give an answer.
Could you please upload your SLD please?

 

[Parchie]

@Histor,

What if all the 10 branch circuits leaks each 60mA which is less than it tripping setting (300/150mA) in DB-02 and it accumulates (10circuits X 60mA = 600mA) lead tripping ELR in DB-01? is it possible?

There are lots of options. You can delete the use of the ELR, if your protection setup allows; you can split your circuit so each branch leakage current cannot go over the ELR current sensitivity; or you can replace those leaky devices with better ones. Either way, the sensitivity of your ELR should be higher than your actual leakage current for smooth operations. Remember, the length of your wire runs could add more leakage current seen by the ELR.

 

[che12345]

@ Mr. Parchie (Electrical)29 May 23 22:43
".....#1. There are lots of options. You can delete the use of the ELR, if your protection setup allows; .....#2. you can split your circuit so each branch leakage current cannot go over the ELR current sensitivity;.....#3... or you can replace those leaky devices with better ones. ....#4. Either way, the sensitivity of your ELR should be higher than your actual leakage current for smooth operations. .....#5. .. Remember, the length of your wire runs could add more leakage current seen by the ELR ".
I am of the opinion:
1. deleting it may not be allowed, otherwise the ELR would not have been there. In addition, it is not a good design without earth-fault protection, depending on over-current/short-circuit protection by MCB; which are at a much higher current value.
An alternative would be add a small time delay in the ELR say <0.4s to bridge the [accumulated] earth-fault current >250mA that may occur for [a short duration of say <0.3s].
2 to 4 are valid advice.
5. it was working fine before. There was no mention that the wiring being extended. However, it is valid that the [leakage current] increases with increase conductor length, but minimal.
Che Kuan Yau (Singapore)

 

[Parchie]

@che,
You missed the first suggestion there. Please read the portion "if your protection setup allows.".