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#28025 - 08/08/03 10:03 AM Double insulated?  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
What, specifically, does this mean?
Or what is the process by which something, such as a hand tool, becomes "double-insulated"?


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#28026 - 08/08/03 11:14 AM Re: Double insulated?  
NJwirenut  Offline
Member
Joined: Sep 2001
Posts: 806
Bergen County, NJ
AFAIK, this refers to insulated wiring contained within a non-conductive housing. Effectively, 2 or more layers of insulation between the user and anything live.


#28027 - 08/08/03 11:23 AM Re: Double insulated?  
SvenNYC  Offline
Member
Joined: Aug 2002
Posts: 1,691
New York City
Sort of like a portable radio in a plastic cabinet, a hair dryer or even an electric drill in a plastic shell instead of a metal one.

The symbol for "double insulated" is two concentric squares.

[Linked Image]

This was a Taiwanese version of the symbol on a pair of speakers (found this one someone's audio review website).

[Linked Image]


#28028 - 08/08/03 12:27 PM Re: Double insulated?  
ThinkGood  Offline
Member
Joined: Aug 2002
Posts: 1,081
Milwaukee, WI


#28029 - 08/08/03 07:21 PM Re: Double insulated?  
sanUK  Offline
Member
Joined: Jan 2003
Posts: 45
Scotland
The UK regs defines it as "Insulation comprising both basic insulation & supplimentary insulation.

Here is more info


#28030 - 08/08/03 09:37 PM Re: Double insulated?  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,223
SI,New Zealand
Double Insulation as I understand it to be, means that there are 2 layers of insulation between the live part and surfaces which are normally touched by the user of an appliance, etc.
The same goes for flex's, although for some odd reason, TV's and the like only use cords with single insulation. [Linked Image]


#28031 - 08/09/03 06:59 AM Re: Double insulated?  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
The electrical regs. in the U.K. have required double-insulated cords (flexes) on appliances since the mid 1970s. There are only one or two exceptions, such as fairy light strings.


#28032 - 08/09/03 07:59 AM Re: Double insulated?  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,223
SI,New Zealand
So why then Paul do TV's, VCR's and Stereo's use single insulated flexes?.
Or is this just a Aust/NZ thing?.


#28033 - 08/09/03 11:13 AM Re: Double insulated?  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
All modern TVs, VCRs, bedside clock-radios, etc. sold throughout Europe are now fitted with double-insulated cords (brown/blue within an overall black/gray/white sheath).

I didn't realize that SPT-type cord was still used in Australia/N.Z. I thought it was still only common in NEMA-based countries.


#28034 - 08/09/03 01:04 PM Re: Double insulated?  
SvenNYC  Offline
Member
Joined: Aug 2002
Posts: 1,691
New York City
Most of our light-duty appliances (TVs, radios, record players, fans) used to come fitted with 18-gauge SPT-1 cord.

In the past couple of decades there was a movement to equip things like TV sets, some hi-fi equipment, blenders, etc. with 18-gague SPT-2 cords. SPT-2 has thicker insulation. SPT-3 is the thickest you can get for parallel cord (at least that I've seen). SPT-3 is normally used for air conditioner extension cords -- normally they're built using 14-gauge wire.

Anyway....in the past - oh I'd say - five or six years, almost all UL-Listed electronic equipment (TVs, radios, tape recorders, turntables) started coming with the following:

NISPT-2 at 18AWG.

I think UL has been one of the ones reponsible for this -- the reason being the insulation is thicker, and less prone to getting nicked. UL-Listed fans and lamps are now being sold with 18AWG/SPT-2 cordage. The fans have had it for years. The lamps, only in the past two or three years or so.

The "NI" stands for Non-Integral. In other words, this is essentially flat SPT-2 cable that is encased in a tough, abrasion resistant thermoplastic jacket. Construction is similar to the thinner European version.

There are also some replacement cord-sets sold for cassette recorders that use NISPT-1 18AWG cord and some no-name cordsets that are actually made with .75 mm harmonized cordage (also double insulated).

Unfortunately, you can't buy NISPT cord in bulk at your local hardware store to replace the cord on your TV set that your dog chewed up.

SPT-2 cord in 18-gague is also pretty difficult to find in bulk. Certain mail-order places, however sell 18AWG/SPT-2 ready-made cordsets with moulded plugs (for replacement use or OEM)

If you're buying bulk zip-cord off the spool in most hardware stores and lighting stores, you're mostly limited to SPT-1 18AWG or SPT-2 16 AWG (used mostly in ordinary extension cords).


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