Organizing Wiring with Load Groups

Load Groups may be needed for safety or functional reasons. The concept applies to both AC and DC

systems.Load shedding is a specific application of load groups

to manage system loads.

Presenters

• Brian Criner – Paneltronics, Inc.•Wayne Kelsoe – Blue Sea Systems (retired)

• Both are members of the ABYC Electrical Project Technical Committee

What is a load group?•For our purposes, it is a group of branch circuits that have some shared characteristic, typically a specific source or return.

•Load groups are not mentioned in ABYC but it is implicit in many of the design requirements.

Load Groups in AC

• Specific load groups such as distribution from dual shore cords or from inverters are required for safety and functional reasons.• Others manage loads that are eligible to be supplied only by specific

sources.• Others, such as using sub-panel distribution, involve good practices to

contain noise, to control voltage drop.• Load Groups can also be a way to organize load shedding to help

control priorities when available power is limited.

Single 240VAC Source – Dual 120VAC Bus

Single 240VAC Source – Dual 120VAC Bus

Dual Shore CordsLoad 1

Load 2

Load 1

Load 2

Dual Shore Cords

• Each group has its own neutral• The safety ground is common, it can be two busses, each connected

to the DC Gnd, or a single bus.• We have been doing this for years, but it can be at risk if a subsequent

installer adds something and breaks the rules.• Returns a neutral to the wrong bus. Will trip ELCI’s• Selects the wrong shore cord, may not create expected function.

Dual Shore Cords

• Can be done with two panels• Can also be done with a single panel divided into groups• Busses are most easily split in distinct columns• Column busses can be segmented, but present more difficulty with marking• Much easier to access the wrong neutral bus when working in a shared panel

• It would really be nice to help differentiate with color codes, but having extra colors in AC is a supply and a convention problem.• Mark neutrals with colored tape.. Blue on Shore 2?• Mark backside of shore 2 breakers with the same color?

“Pass Through” Inverters

ACIN

G

N

H

DC

HACOut

N

Non-InverterLoad

Inverter Load

Pre-Inverter Neutral

Inverter Neutral

“Pass Through Inverters”

• Some loads are inappropriate to feed from an inverter• Some auxiliary battery chargers (handy for charging specialty batteries)• Water Heating• Space Heat and Air Conditioning

• This leads to the Pre-inverter and Post-inverter Neutrals• The neither neutral can be grounded on the boat when shore power is in use.• The post inverter neutral should be grounded when the inverter is the source

of power and this is usually handled inside the inverter/charger if it is a marine inverter.

Common Errors

• Connecting a Pre-inverter load to the Post-inverter neutral.• Will appear to function normally• Could ground the shore neutral temporarily during the transition to shore

power!• Depending on dock wiring, large circulating current can flow from dock

neutral to ground.

• Connecting a Post-inverter load to the Pre-inverter neutral.• Will not function when in inverter mode.• Could back feed, causing shore input neutral to be “hot” to ground during

inverter operation, causing a shock hazard!

A “non-pass through” inverter

• Inverter’s that don’t pass through AC when available can be used with a manual selector switch.• This allows the inverter’s output to be grounded, but kept separate

from the shore neutral.• Same considerations for applying loads to appropriate neutrals apply

MAIN DISTRIBUTION PANEL

MAIN DISTRIBUTION PANEL

MAIN DISTRIBUTION PANEL

Inverter without Automatic Transfer

Non-InverterLoad

Inverter Load

Pre-Inverter Neutral

Inverter Neutral

INVERTERCHARGER

AC

G

N

H

DC

Add in a GenSet

ACIN

G

N

H

DC

HACOut

N

Non-InverterLoad

Inverter Load

Pre-Inverter Neutral

Inverter Neutral

Adding the GenSet

• Did not introduce any new load groups in this configuration.• Did add a source selector

Now we add a load group for the GenSet

ACIN

G

N

H

DC

HACOut

N

Non-InverterLoad

Inverter Load

Pre-Inverter Neutral

Inverter Neutral

Gen Only Load

GenSet only Neutral

GenSet only Load Group•We see this on commercial fishing boats• The refrigeration system requires more power than the shore cord

can handle.• Other possible loads may be larger air conditioners or anything not

to be used in port.

• Alternative is run through main panel and post operator instructions not to use on shore power.. Prone to error.

Isolation Transformer with GenSet

Load

Isolation Transformer with GenSet•Hey, that is only one load group.•Why talk about that?

•Well, in older boats we see a variation on the theme that is a bit disturbing.

It is tempting to tie all neutrals common and use single pole source selection!

Load

Now we have circulating currents in the Ground• This is pretty easy to find on older boats•Generally the circulating current will not exceed wire

capacity• This can cause voltage drop in grounds and

differences in ground potential

This could be fixed with a single point grounding of the neutral at the common bus.

Load

Using a single tie between Neutral and Ground would call for an exception to E-11• Instead of grounding the neutral at the source of power• Ground the Neutral at the common bus

• If you have to work on a boat like this, consider single point grounding of the neutral rather than a major rewire.

Sub-Panels create load groups

Load

LoadAC

Source

Main

Sub Panel load groups

• That looks pretty obvious• How can we mess that up?• Taking a short cut from a branch load back to the main neutral

or to the main ground can increase noise and magnetic fields.

Neutral “Shortcut”

Load

LoadAC

Neutral “Shortcut”• Example: Water heater is in engine room near main panel, but feed is

from sub panel near the galley for ease of control.• Well meaning installer shortcuts the neutral to the main neutral bus

to shorten wiring.• The big wire loop generates a magnetic field proportional to the area

enclosed.• These AC magnetic fields can induce currents in nearby metal• If wires pass separately through a metal bulkhead or enclosure the circulating

current can even start a fire!

• The same mistake in a DC system generates DC magnetic field, compass error and also transmits noise

Ground “Shortcut”

Load

LoadAC

Ground “Shortcut”

• What is the harm, grounding wires are not normally current carrying?• In power electronic devices such as battery chargers, many of the capacitors

in the EMI filters return to the case ground.• The filter current is noise current being directed to ground to reduce voltage

changes on the case of the product.

• Again, the noise currents from EMI filters can occur in DC systems• Good practice to bundle hot, neutral and ground or Plus, Minus and Ground

in single cables or bundles.

DC Load Groups• We talked about pairing feeds and returns as it applies to both DC and

AC distribution.• Other DC load groups are common wherever different battery

systems are involved: Engine Start, House, Inverter, Bow Thruster, etc.• Less obvious are• Noise Sensitive vs. Noise Producing devices, may require distinct feeders and

returns.• Vital service such as navigation and communications with distinct source

switches to choose the best available source.• Loads that tolerate voltage drop distinct from those that are tolerant.

Basic DC Load Groups – House + Start A lternator

Starter

Engine

Adding 24 Hour CircuitsA lternator

Starter

Engine

24 Hour Loads#2 Bilge Pump

Bilge AlarmCharger Connection

24 Hour CircuitsMain Bilge Pump

Radio PresetsCourtesy Lights

Charger ConnectionSecurity Alarm

MAIN BATTERY SWITCH PANEL

MAIN BATTERY SWITCH PANEL

MAIN DC BREAKER PANEL

MAIN DC BREAKER PANEL

Load Shedding• Manual• Need Ammeters for AC• Need Voltmeter or State of Charge Meters for DC• Meters with Alarms more effective than just indicators

• Automatic• Dedicated switch devices in line with specific loads• Meters with alarm outputs that can drive relays• Digital Switching Systems that can be programmed for load shedding• Smart Inverter/Chargers that cut charging current when other loads are high

AC Meters for Manual or Automatic Load Shedding

Alarm Alarm plus Relay Out

DC Meters for Manual or Automatic Load Shedding

AlarmAlarm plus Relay Out

Load Shedding – Dedicated DevicesExample:

Low Voltage Disconnect for DC

Useful for removing low priority loads

Example: Audio Systems on Ski and Wake Board boats without dedicated house batteries.

Load Shedding – Panel Groups

•When laying out a panel, low priority loads can be grouped for manually disconnecting

•Panel feeders can be cut, so dedicated devices or relays can drop out more than one circuit at the panel

Load Shedding – Digital Switching• Digital Switching systems with measurement capability can be

programmed to shed loads

• Examples are C-Zone, Carling ECS III, ETA PowerPlex, EmpirBus

• See individual manufacturers for capabilities, availability• Many of these systems are targeted to OEM installation in larger boats.• May or may not be suited to retrofit.

Load Shedding – Inverter-Chargers• Mastervolt, Xantrex, Victron and possibly others have

inverter/chargers that reduce charger load as AC line is overloaded.• Unless there is an input for external metering, all AC must pass

through the inverter• This is different from the load group discussion earlier that isolated non-

inverter loads• Some units pass power for the non-inverter loads through the inverter for

purposes of measurement, integrates with the load group panel design discussed earlier.

• See manufacturers here at the show for specific capabilities

AC LOAD SHEDDING Purpose in Life

Eliminates nuisance tripping of shore main (dock and vessel) and generator main by momentarily shedding and

then restoring loads

AC LOAD SHEDDING• System will automatically shed loads when total current draw from shore

or generator exceeds a preset threshold• Automatically restores power to shed loads when total current drops

below the threshold• Should be easily integrated into existing or new Marine electrical power

distribution systems• Display can be remote mounted to better accommodate existing systems

SYSTEM COMPONENTS

DISPLAY INTERFACE

120VAC TURNKEY ASSEMBLY

SYSTEM INSTALLATION

SYSTEM INSTALLATION

Any Questions?

Thank You!