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Old 03-04-2013, 03:13 PM   #32
Gnarly Adventurer
Joined: Mar 2008
Oddometer: 154
Originally Posted by dholaday View Post

You clearly know a lot about wiring, certainly more than I, and more than enough to confuse me. Especially since we are talking in generalities over time-lagged forum postings.

But marine-grade wire is tinned AWG, not SAE plain copper. And boats move around a lot, and flex, and are subject to vibration and weather, and seem more like a sidecar rig to me than they do to a house.

Re fuses - most of the gear I've seen has a fuse with an amperage rating higher than the actual current draw of the attached device. Heated gear is a good example. So is a GPS. And Aux lighting. And Auxiliary power plugs. Seems like the fuse is there to protect the wiring rather than the device.

I understand that I should not attach a 15-amp device to a 22-gauge wire with a 5-amp fuse. But I don't see anything wrong with attaching a 5-amp device to a 16-gauge wire with a 15-amp fuse.

Confusing matters further is that my GS runs on a CANBUS and thus has no fuses except for those various owners have put on. I haven't the foggiest idea on how to figure out how BMW has 'fused' the OEM wiring, or what effect tapping relay trigger wires into that wiring might do. But we all still do tap into the OEM wiring for LOTS of things - and the roadside is not littered with burnt out hulks.

Maybe if we can bring the conversation down to specific applications, rather than generalities, I can become less confused.

I hesitated before replying in the first place. My intention is to help others with problems, including attempts at explanations to increase overall understanding of a system or technique etc. The less a person may know on a given subject the more I'll try to explain. Sorry if it gets wordy when I get carried away. I also add info so someone doing archive search may be helped.

Of the wire types commonly available there are two basic types. One type is Residential, Commercial and industrial wire, which I was referring to as 'AWG', after the National Electrical Code 'American Wire Gauge'. AWG may be listed as various descriptions from TW, THHN etc. to futher clarify what I was referring to. It's the wire normally found at local hardware stores labeled TW [most common], TWN, THW and sometimes THHN which has additional clear nylon outside sheathing.

AWG isn't the exact nomenclature of wire types but is common, somewhat like a sidecar is called a hack or a tub. I know of well over 100 particular types of electrical wire with specific nomenclature describing alloy, coating, sheathing, protective, usage and size categories. There's probably three or four times that many out there but no point in further sub-categories for sake of brevity and simplicity. AWG shouldn't be used on vehicles.

Generally the other common type is automotive wire, referred to here as 'SAE', after Society of Automotive Engineers, which doesn't use the descriptions TW, TWN, THW etc. Automotive 'SAE' wire contains more strands of finer thickness in a particular gauge size than 'AWG' wire such that it's more flexible. May also be different alloy than 'AWG' wire and uses different insulation coatings. SAE wire gauge size is not the same as AWG, SAE being smaller overall outside diameter per gauge. That affects the use of strippers and how well they perform without damaging wire. SAE gauge strippers will damage 'AWG' wire conductors and solid wire strippers will damage multi-strand wire.

One of the stronger automotive types is HDT. GXL isn't as thick insulation but is more flexible. SXL is the common wall thickness of insulation usually found. GPT is the most common automotive retail store type. HDT is a good choice for motorcycles and some marine apps [other than actual Marine grade wire] if kept from extreme heat. In general, Marine wire such as Ancor is a good choice per specification when in doubt. Some but not all Marine wire is tinned. CAN-Bus is sized according to SAEJ1939, yet another type and Metric, has much larger minimum bending radius.

Fuses are sized to protect the circuit to prevent damage. Attaching a 5-amp device to a 16-gauge wire with a 15-amp fuse will protect the wire circuit but not the device. Also depends on where fuse is located, at source or just before individual device as to what's protected.

Info on general wire types:

This site incorrectly implies that SAE wire is the same gauge as AWG gauge:

Automotive types, after SAE Specs:

Excellent Marine info with size warning, shows difference in Mean Circular Mils of SAE and AWG:

Beyond earthly wire:

A common problem with wiring nowadays is foreign mfd. products. Metric and ISO 6722 measures don't match American SAE J1128 or AWG inch/foot, never can. Products sized to one system don't precisely match the other. Both wire and wire tools may be sized metric or 'American', often causing mismatched tools to nick or cut conductors under coatings which weakens wire and lowers conductivity. Added to differences in actual gauge size in wire types it becomes more serious. I prefer Klein tools.

Another potentially serious problem comes from abrasion caused by loose or incorrect wire ties and clamping devices. Proper tie-wraps or restraints are critical in cycle wiring. Nylon tie-wraps can cut right through many common wire coatings so it's real important to get them very tight to prevent movement and abrasion. I like to wind a couple of wraps of Scotch 33+ or Scotch Temflex 1700 around the wires or bundles before tie-wrapping to further guard against wear and abrasion.

I spent a lifetime working with various different electrical systems, controls and wiring of all sizes and types so I have more than a passing familiarity with wire, wiring and devices. There are many different working standards governing wire types all with their own specifications and peculiar nomenclature. I stuck with the terms already used in the thread so as not to pour in more confusion. Because I have some experience there I thought I might be able to help, sorry to confuse.
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