I do not have a copy of this standard, so I cannot speak directly to it, but in general, when one is concerned with whether or not a 3ph load is balanced or not, it is for one of 2 reasons:
1. Load calculation- If your total power is expessed in kW or kVA, then when you translate this into amps for the purpose of fuse size, the overcurrent protecter size will increase as the imbalance increases. Consequently the conductor size will increase. Example, you have a 120/208Y 3 phase machine rated at 36kW. If the load is perfectly balanced, the demand will be 100 amps on each leg. But if the load is out of balance, the three legs could look something like, 75-100-125 . You would have to fuse for the highest leg. 2. Neutral conductor size. The neutral conductor size is a function of the greatest possible imbalance between any 2 legs. -------------------------------------- List-Post: [email protected] Date: 6/14/96 2:49 PM To: Keith Gershon From: Max Received: by ehssmtp.lbl.gov with SMTP;14 Jun 1996 14:49:13 +0100 Received: from lbl.gov (lbl.gov [128.3.254.23]) by ehssun.lbl.gov (8.6.12/G) with SMTP id OAA25477 for <[email protected]>; Fri, 14 Jun 1996 14:49:41 -0700 Received: from mail.ieee.org (rab.ieee.org) by lbl.gov (4.1/1.39) id AA17117; Fri, 14 Jun 96 14:49:05 PDT Received: by mail.ieee.org (8.7.3/8.7.3) id OAA11227 for emc-pstc-list; Fri, 14 Jun 1996 14:16:56 -0400 (EDT) Message-Id: <[email protected]> To: [email protected] Subject: "Balanced Three-Phase Equipment" List-Post: [email protected] Date: Fri, 14 Jun 1996 12:16:06 -0600 From: Max <[email protected]> Sender: [email protected] Precedence: bulk Reply-To: Max <[email protected]> X-Resent-To: Multiple Recipients <[email protected]> X-Listname: emc-pstc X-List-Description: Product Safety Tech. Committee, EMC Society X-Info: Help requests to [email protected] X-Info: [Un]Subscribe requests to [email protected] X-Moderator-Address: [email protected] I have an old, draft copy of IEC 1000-3-2. In the definitions section (section 3.14), it states the following: 3.14....Balanced three-phase equipment Equipment having rated line currents which differ by no more than 20%. Then in section 4, it classifies equipment in two 4 classes and under Class A, it says: Balanced three-phase equipment and all other equipment except that stated in one of the following classes: So, what this seems to be saying is that both "balanced" and unbalanced equipment falls under class A (if the equipment has an input power greater than 600W. I'm not really very familar with safety regulations, but this doesn't seem to make any sense to me. What is the significance of balanced three-phase equipment? What are the issues involved if the equipment presents an unbalanced load? Are there any requirements in Europe that require current balancing? Thanks, Max [email protected]
