BUS BARS or CABLES ?

7/7/15

BUS BARS or CABLES

Super Flex Cable with Hot Formed Lugs.

Double Laminated UL Approved Bus Bar

BUS BARS or CABLES

1. When should we choose to deploy power cables ?

a) When costs are the greatest concernb) When space is availablec) When using bus bars offer no tangible advantaged) Where cable flexure is necessary

2. When should we choose to deploy Bus Bars ?

a) When cable routing produces too many design constraints b) When the space available is not enough to pass cablesc) In complex areas which demand power to be fixed in placed) When Blind Mate Power is needede) When bolt in modularity yields configurability & servicabilityf) When safety issues arise due to disconnected cables moving in close proximity to other live circuits.

BUS BARS or CABLES

When choosing cabled solution what considerations should be considered ?

a) In the space available, will the cables have the bend radius necessary for the system it goes into ? Work hardening of the copper can yield higher impedances which create hot spots in the cable and possible arc flash issues may occur if the cable jacket melts.

b) Cable Manufacturers have heard the clarion call for high strand count cables, which are sometimes called “super flex”. For example, it is now possible to obtain a 4/0 Cable with strand counts as high as 6,000 strands. Depending upon the cable jacket this can yield from 3-6 inch bend radii.

BUS BARS or CABLES

Here we see a bus bar in a gap which 4/0 cables would not easily pass through. So tier to tier cabling is easily done in addition to being safer.

(Isulative Lug Boots not shown in this view. All double lugged bus bar connections were booted for safety).

BUS BARS or CABLES

This is a modular bus bar module. The module was created to keep the equipment height below the required level.

Additionally, a lever was employed which easily overcame the insertion forces of the Blindmate connectors.

Using this technique, high current UPS systems can become modular and reduce the downtime when in need of repairs.

BUS BARS or CABLES

Conversion from Cables to Bus Bars.

Diameter in inches x .7854 = in^2

.46 x .7854 =.361

.46” Diameter

1”

4/0 Cable Bus Bar .361”

Conversion from Bus Bars to Cables.

in^2 x 1.2745 = Diameter

.361 x 1.2745 = .46

BUS BARS or CABLES

Based on 2005 NEC, Table 310.16. For different ambient temperatures than the one shown above, consult the NEC tables.

BUS BARS DESIGN

Bus Bar Safety / UL

BUS BARS DESIGN

UL requires double insulation on Bus Bars. The laminated Bus Bars have two layers between the chassis surface and the interstitial layers have two insulators. The top layer also has two insulators. The edge requirements for insulation require a pinch seal of the insulators or and edge fill with epoxy. Both methods are viable for insulating the edges.

Bus Bar Insulation Requirements

BUS BARS DESIGN

The connectors on the PCBA below require +/- .005” socket to Socket tolerance. A ganged fixture was created to hold the pins before insertion into the buss bar assembly thus achieving tolerances of approximately +/-.003” pin to pin.

Low insertion force 65A connectors Bus Bar 3mm mating pins

Bus Bar Pin & Socket Tolerances

BUS BARS DESIGN

Bus Bar & Insulation Stack

Total Thickness: 299 mils

Insulation: Mylar 6 mils

Adhesive: Thermal 1 mil

Bus Bar: Tough Pitch Electrolytic Copper (80 mils shown)

Insulator with 1 layer of adhesive

Insulator with 2 layer of adhesive

Copper Bus Bars

NOTE: I prefer using an insulator as opposed to paint because painted bus bars don’t offer tight tolerances. Additionally there are quality control issues with paint thickness control.

BUS BARS DESIGN

A

B

Bus Bar Creepage for 48V or less

If distance A + B are > 2 mm = Passable Clearance

NOTE: This takes into the Air & dielectric strengths over the distance. I used 3 mm in my designs to err on the side of safety.

BUS BARS DESIGN

A

Bus Bar Clearance for 48V or less

If distance A is > 2 mm = Passable Clearance

Bus Bar

UL 94V-0 Glass Filled PC Bushing

Top & Bottom Bushing

NOTE: This takes into the Air & dielectric strengths over the distance. I used 3 mm in my designs to err on the side of safety.

BUS BARS DESIGN

Bus Bar

Interstitial Insulation alternatives

Thank You !

BUS BARS DESIGN