Electrical surges are a little understood and seldom considered aspect of owning and maintaining a boat.  Indeed, if you never go to a dock, you probably don’t need to concern yourself with Surges.  But, if you are like most boat owners and go to the dock on occasion (or live on one) and plug into shore power, you should be very interested in them.

Contrary to popular belief, small marine generators are seldom the cause of Electrical Surges.  They may be the source of high voltage or low voltage, but seldom surges.  In very high, or very low voltage situations, the breaker protecting the circuit should open and protect the items downstream.  That said, marginally high (swells) or low (sags or brown outs) voltages don’t usually trip a breaker.  For those, you need a buck/boost transformer.  But that is another subject.

Surges are one of the most common problems we experience with utility voltage in the Caribbean.  They are insidious because they usually come and go without a trace other than damaged electronic equipment.  A surge is high voltage incident of very short duration.  They may be up to 20,000 volts, but last less than 2 milliseconds with a frequency of up to 20 MHz.  This is much faster than a breaker is designed to react to.  The result is often disastrous to electronic equipment.

Surges can be the result of either natural or man-made causes.  One of the most common sources of surges is lightning striking a utility pole, line or transformer.  The resulting surge travels down the utility line looking for a grounding source.  Very common causes of surges in the Caribbean come from the Electrical Utilities themselves.  Generators shutting down without opening a breaker and transformers crashing to the ground due to vehicle impact or wind are common causes.  Even equipment connected to the grid such as imaging equipment, load switching, and large SCR loads can cause surges.

Surge Protection Devices (SPD) or Transient Voltage Surge Suppression (TVSS) reduce the voltage in a surge.  They are self-sacrificial devices that “shunt” the voltage to ground.  But any SPD will only do so much.  There is always “let through” current.  So, if there is a 20,000 volt surge that goes through an SPD, it will knock down the surge to perhaps 6,000 volts.  But that let through current is still enough to damage sensitive electronics.  Therefore it is always a good idea to have “cascaded” surge protection; that is a secondary and possibly tertiary level of protection before the “load”. 

Most SPDs are made from what are called Metal Oxide Varistors (MOV).  These are small epoxy encapsulated discs of various diameters that redirect the surge to ground.  SPD’s are rated by the number and size of MOV’s they contain and so how many “hits” they will take before they fail.  All good SPD’s have indicator lights on them indicating whether they are protecting or not.  Usually green indicates that they are protecting and red means that one or more of the MOV’s on that leg have burned out.  That is your indication to replace the SPD.  SPD’s are rated in KA, the higher the number the longer they will live.  There are SPD’s on the market that are rated at 350KA and higher.  It is generally accepted that a 250 KA SPD will last a lifetime in the worst conditions though.  That said, 150, 100 or even 50 KA will protect equipment for many years.  The bottom line is to get at least 2 SPD’s of any rating depending on your budget and mount it where it can be monitored periodically.

There are many other features which add to the value, and cost, of SPD’s.  These include remote monitoring, surge counters, “noise filters” for transient noise that can cause damage to very sensitive electronics, and more.  But, for most marine applications, these are seldom a consideration.

If surges are so common, why don’t we have electronics failing every time there is a lightning storm or a pole mounted transformer taking a tumble?  The reason is that most electronic equipment has MOV’s in them. You have almost certainly seen the little blue discs on circuit boards and in computers and other electronics.  Those are MOV’s. The MOV’s in your equipment do their job for a while.  But most are not designed to take repeated and frequent surges, and so they burn out.  They are not designed to be the first line of defense against surges and therefore electronics manufacturers seldom put indicator lights on their MOV’s.  It is an added expense in a price competitive market.  If the MOV’s get the device through the warranty period, they’ve done their job.

So, anytime your vessel is plugged into shore power it is subject to the vagaries of the Electrical Utility bus.  Your computer, battery charger, water maker, microwave, electronic cooker and any other AC electrical device is subject to damage due to a surge.  Some upper end marinas do put SPD’s in the power pedestals, but that is just the first level (called Type 1) SPD.  Remember there will always be let through current.  Whether there is enough current in there to create damage depends on the voltage of the initial surge and the condition of the MOV’s in your electronics.  Remember they will almost never tell you if they are working or not.

But installing SPD’s is expensive right?  Wrong.  A 150 KA SPD can usually be purchased for well under $200.  80 KA and 50 KA should cost less than $100 depending on whether you have single or three phase power and what other options are installed as well.  So the equipment costs are extremely modest compared with the protection they offer.  Installation is not difficult, although some level of experience with AC electricity is important for safety reasons.  The only trick is to make the electrical run as short as possible and twist the wires from the SPD to the electrical bus on your boat.  Most SPD’s come with 18” wires, but that is for convenience sake.  You should mount the SPD as close to the bus as possible to the bus and cut off the excess wire.

So, Surge Protection is cost effective, it is relatively easy to install and can save you hundreds, if not thousands, of dollars.  It’s sort of a no-brainer.  Just be sure to purchase a reputable brand that has indicator lights on it.  There are some real budget products on the Market that are of questionable value.  We recommend Eaton Electrical SPD’s.  They are cost effective and Eaton is one of the Market Leaders in both research and state of the art, quality products.

Give any of Parts & Power’s knowledgeable sales people for more information and prices.  


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Parts & Power is the premier supplier of Marine and Industrial equipment and spare parts in the Caribbean.

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