I have two questions for che12345:
a. If the Incomer breaker fails to trip and the upstream Swgr breaker trips, the let through energy still far exceeds the Incomer MCCB short time withstand rating. So how is this fine?
b. For Incomer MCCB to cooridnate with the feeder breakers, the feeder...
This question is specific to a MCC Incomer where ABB MCCB is being used rather than an ACB.
The MCCB short ckt interruption capcity is 70kA at 380V. But its short time withstand rating is only 7.3kA at 1 sec.
Now the prospective short circuit current at the MCC bus is 62kA.
If the Manin Incomer...
Hello Waross I have the 2021 version of CEC which covers in Rule 8-102, the requirements of voltage drop.
In Rule 8-102 (2) the Code recognizes the need to size the feeder or branch circuit as per the actual load seen by the circuit (and not the nameplate rating):
"Notwithstanding Subrule 1)...
Hello Bill... Yes you are correct. But CEC unlike NEC also allows variances and a qualified engineer can use the shaft kW value to reduce the load amps to actual value, and show that the permissible voltage drop is maintained. This as I said above is one of a case, not a general practice.
I have a simple question. Does any Code or Standard or any guideline ever specify that voltage drop of motors needs to take into consideration: a. Full load Amps (Nameplate rating) and b. Resistance of the conductor needs to be at the max temp of its insulation i.e 90degC? . The reason I ask...
Thanks xnuke & dpc. The main reason for this query is: At a later point, say 10 years down the line, when we add loads, an adequacy check is always done. This check is only on the Transformer capacity and not on the downstream bus / breaker. If we choose lower than the 125% rated value of the...
Grades of release as defined in API RP 505 is:
Continuous : 1000 or more hours/year
Primary: 10 hours/year to 1000 hours/year
Secondary: less than 10 hours/year
In your case it appears to be an engineering judgement between Primary & Secondary.
This relates directly to Zone 1 or 2.
Even if you...
I believe that NEC Article 450.3 Overcurrent Protection (and Table 450.3) directly determines the secondary side breaker sizing (and bus sizing).
For example, if I have a 2500kVA, 13.8-0.48kV Transformer, the rated secondary side current is 3007A. As per Table 450.3, for 480V secondary (<1000V)...
Once again posting this question for NEC based power distributiin design: Is it required for NEC based designs to use Equipment Grounding Conductor?
Article 250.36 High Impedance Grounded Neutral systems does not mention it (see A to G). Similarly, later in Part VII Methods of EGC Connection...
Considering the Ampacities as given in IEC 60364-5-52, and the derating factors given in this std, you are still good with a 4 sq.mm cable, based on ampacity. Method D - laid in ducts, Method D2 - laid in ground and Method E - laid in tray give ampacities 35A,39A and 42A reply. You may take 6...
Has there been any publication for loop impedance calculations under NEC environment, identical to IEC or BS 7671? The table 250.122 in NEC provides the minimum EGC size for particular breaker. Is this size linked with loop impedance? Over and above voltage drop, do we need to establish loop...
After working in the industry for 30 yrs, many of us have our own personal libraries of spreadsheets, which we unleash at the right time. Try to develop your own sheets based on your requirement. If you are working in consulting engineering, you should be having access to most of these spreadsheets.
Another point to be noticed, Sec 250.187 which deals with High impedance systems for greater than 1000V, clearly identifies Equipment Grounding conductor in Sec 250.187 (D). But any such EGC reference is not there in Sec 250.36 (A) to (G). I rest my case.
Dear che12345...I am thinking on similar lines. I am attaching the handbook excerpt of NEC Sec 250.36 which deals with high impedance system. The clear requirement is for ground fault detection (as earlier mentioned by me). The presence of equipment bonding jumper (with mention of equipment...
Parchie...the reference here is not normal domestic or industrial plants which can tolerate tripping the circuit on ground fault. The discussion here is for numerous process plants where no tripping for L-G fault is tolerated, without a decision taken by AHJ.
Che Kuan Yau.....I have used High impedance grounded systems in most of the process plants which need continuity. NEC is clear about the purpose for EGC. But I am questioning the need of return path through EGC where we are operating the load with ground fault. The modern day Core balance CT...
Right now I don't have the Code book, but I believe that NEC requires the equipment grounding conductor for resistance grounded systems also. What is the rationale behind this? For eg. for a LV system with 10A resistor, we would only be detecting GF current using CBCTs and only for detection...
Thanks all for your inputs. In this particular plant, all UPSs have floating neutral in the outgoing 120VAC 1ph circuits with no intentional earth connection. Thus, several kms of UPS distribution network is operating with floating neutral. Now, possibly, in old DCS / PLC, the voltage power...
I have a 80kVA UPS (Chloride Apodys) with 120VAC, 1 phase, 60Hz output. Its a double redundant system with isolation transformers on the output side. The measured voltage at one of the consumer end is: L-N : 115VAC, N-G: 85V, L-G = 115VAC. This is a floating neutral system. The O&M Manual for...
The estimated current at 700kW is 1150A. I am assuming that you are using 2 runs of 120sq.mm or 150sq.mm Cu conductors.If you are using industry standard Cu connectors (like NEMA two hole) lugs, then you should be ok.Possibly the vendor did not follow the standard openings. I wonder if it's two...
