有份筆記供參考 "在第二章，低壓配電電器內有詳細解釋" 。
水喉佬上
一個機電署的電郵，說明 4.5KA 未必足夠。Re: 回信: MCB backup protection by BS88 fuse.2010年1月26日 星期二 下午5:17
寄件人: "Steve WONG" <sytwong@emsd.gov.hk>收件人: "Kents Chu" <kentskkchu@yahoo.com.hk>
Dear Mr. CHU,
As discussed on phone, the breaking capacities shown in Table 9(2) are minimum values
(最低數值) and are for
general reference only.
(供一般性參考作用)Regards,
Steve Y. T. WONG
for Director of Electrical and Mechanical Services
寄件人: sytwong@emsd.gov.hk <sytwong@emsd.gov.hk>
主題: 回信: MCB backup protection by BS88 fuse.
收件人: kentskkchu@yahoo.com.hk
日期: 2010年1月20日,星期三,下午7:36
Dear Mr. CHU,
Thank you for your email.
Please be advised that the minimum breaking capacities of 4.5kA shown in Table 9(2) are for back-up fuses up to 160A, while 160A fuse is used in your example. As stated in Code 9C(2)(c), the breaking capacities of protective devices against fault current should be assessed for all installations, and Table 9(2) is for
general guidance only.
(含有引導/指導性意思)Please contact me at xxxx xxxx if you have any further enquiry.
Regards,
Steve Y. T. WONG
for Director of Electrical and Mechanical Services
----- 轉呈者 ACORD/HQ/EMSD 於 05/01/2010 09:44 -----
Kents Chu <kentskkchu@yahoo.com.hk>
05/01/2010 09:38 收件人 info@emsd.gov.hk
副本抄送
主旨 MCB backup protection by BS88 fuse.
Dear Sir,
Happy New Year to all EMSD staff. My name is Kents Chu, is an REW. At the end of last year 2009, I attended a technical seminar in “電器工會”. The instructor introduced how to apply Earth Fault Protection in LV system. At the same time, the backup protection by HRC/HBC BS88 fuse was mentioned in the class and quoted your's COP table 9(2). He said that using up to 4.5KA breaking capacity MCB with backup protection by not exceeding 160A rating BS88 fuse is high enough to coordination in any circumstance.
On my personal opinion, the peak let-through (peak cut-off) current of BS88 fuse is also high over 10KA within half-cycle even if 160A BS88 fuse. 4..5KA breaking capacity is set to minimum requirement. In many cases 4.5KA breaking capacity of MCB is incapable to cater for that. I enclosed my working example for your consideration & comment.
I will be grateful if EMSD staff can give me a correct answer for my doubt. Please feel free to contact us by telephone of tel:xxxxxxxx if you have any queries.
Thank you for your attention.
Kents Chu
